#include <bits/stdc++.h>
#define MAX_N 1000000
using namespace std;
const int sqrInf = (1e9) - 1;
int n;
string a, b;
int rez;
int dp[MAX_N + 1][16];
void readFile()
{
cin >> n;
cin >> a >> b;
a = " " + a;
b = " " + b;
for(int i = 1; i <= n; i ++)
{
a[i] -= '0';
b[i] -= '0';
}
}
int p[4][2];
///ON OFF T
vector <int> g[MAX_N + 1];
void add(int a, int b)
{
g[a].push_back(b);
}
struct elem
{
int a, b, c;
bool operator == (elem &x)
{
return (a == x.a && b == x.b && c == x.c);
}
};
elem f[16];
int cod[16];
int r[16][2];
void preCalc()
{
p[1][0] = p[1][1] = 1;
p[2][0] = p[2][1] = 0;
p[3][1] = 0;
p[3][0] = 1;
cod[0] = 0;///000
cod[1] = 1;///001
cod[2] = 2;///010
cod[3] = 4;///100
cod[4] = cod[5] = 3;///011
cod[6] = cod[7] = 5;///101
cod[8] = cod[9] = 6;///110
cod[10] = cod[11] = cod[12] = cod[13] = cod[14] = cod[15] = 7;///111
r[0][0] = 0;
r[0][1] = 1;
r[1][0] = r[1][1] = 1;
r[2][0] = r[2][1] = 0;
r[3][1] = 0;
r[3][0] = 1;
r[4][0] = r[4][1] = 0;
r[5][0] = r[5][1] = 1;
r[6][0] = r[6][1] = 0;
r[7][0] = r[7][1] = 1;
r[8][0] = r[8][1] = 1;
r[9][0] = r[9][1] = 0;
r[10][0] = r[10][1] = 1;
r[11][0] = r[11][1] = 0;
r[12][0] = r[12][1] = 0;
r[13][0] = r[13][1] = 1;
r[14][0] = r[14][1] = 0;
r[15][0] = r[15][1] = 1;
for(int i = 1; i <= 15; i ++)
add(i, 0);
for(int i = 4; i <= 7; i ++)
add(i, 1);
add(4, 2);
add(5, 2);
add(8, 2);
add(9, 2);
for(int i = 6; i <= 9; i ++)
add(i, 3);
for(int i = 10; i <= 15; i ++)
{
add(i, 1);
add(i, 2);
add(i, 3);
}
add(10, 4);
add(10, 6);
add(10, 8);
add(11, 4);
add(11, 9);
add(11, 6);
add(12, 6);
add(12, 8);
add(12, 5);
add(13, 7);
add(13, 5);
add(13, 8);
add(14, 4);
add(14, 9);
add(14, 7);
add(15, 5);
add(15, 7);
add(15, 9);
f[0] = {0, 0, 0};
f[1] = {1, 0, 0};
f[2] = {2, 0, 0};
f[3] = {3, 0, 0};
f[4] = {1, 2, 0};
f[5] = {2, 1, 0};
f[6] = {1, 3, 0};
f[7] = {3, 1, 0};
f[8] = {2, 3, 0};
f[9] = {3, 2, 0};
f[10] = {1, 2, 3};
f[11] = {1, 3, 2};
f[12] = {2, 1, 3};
f[13] = {2, 3, 1};
f[14] = {3, 1, 2};
f[15] = {3, 2, 1};
}
int cost[16][16];
int Cost(int a, int b)
{
int c = 0;
for(int x = 0; x <= 2; x ++)
{
if((((1 << x) & cod[a]) == 0) && (((1 << x) & cod[b]) != 0))
c ++;
}
return c;
}
int viz[16];
int que[16];
int getCod(elem x)
{
for(int i = 0; i <= 15; i ++)
{
if(f[i] == x)
return i;
}
return -1;
}
int bagaSt(elem &x, int i)
{
x.c = x.b;
x.b = x.a;
x.a = i;
return getCod(x);
}
int bagaDr(elem &x, int i)
{
if(x.a == 0)
x.a = i;
else if(x.b == 0)
x.b = i;
else
x.c = i;
return getCod(x);
}
int bagaMid(elem &x, int i)
{
x.c = x.b;
x.b = i;
return getCod(x);
}
void bfs(int s)
{
memset(viz, 0, sizeof(viz));
int st = 1, dr = 0;
for(auto u : g[s])
{
que[++ dr] = u;
viz[u] = 1;
}
que[++ dr] = s;
viz[s] = 1;
int c = 0;
while(st <= dr)
{
int cr = que[st ++];
if(cr <= 10)
for(int i = 1; i <= 3; i ++)
{
elem x = f[cr];
c = bagaSt(x, i);
if(c != -1 && viz[c] == 0)
{
cost[s][c] = cost[s][cr] + 1;
viz[c] = 1;
que[++ dr] = c;
}
x = f[cr];
c = bagaDr(x, i);
if(c != -1 && viz[c] == 0)
{
cost[s][c] = cost[s][cr] + 1;
viz[c] = 1;
que[++ dr] = c;
}
if(cr >= 4 && cr <= 9)
{
x = f[cr];
c = bagaMid(x, i);
if(c != -1 && viz[c] == 0)
{
cost[s][c] = cost[s][cr] + 1;
viz[c] = 1;
que[++ dr] = c;
}
}
}
}
}
void getCosts()
{
for(int j = 0; j <= 15; j ++)
{
cost[0][j] = Cost(0, j);
cost[j][0] = 0;
//cout << "LA " << j << " " << cost[0][j] << "\n";
}
for(int i = 1; i <= 15; i ++)
{
bfs(i);
// for(int j = 1; j <= 15; j ++)
// cout << " DE LA " << i << " La " << j << " " << cost[i][j] << "\n";
}
}
void getDp()
{
for(int i = 0; i <= n; i ++)
{
for(int j = 0; j <= 15; j ++)
dp[i][j] = sqrInf;
}
dp[0][0] = 0;
for(int i = 0; i < n; i ++)
{
for(int j = 0; j <= 15; j ++)
{
if(dp[i][j] != sqrInf)
{
//cout << " SUJNTEMN " << i << " COD " << j << " DP " << dp[i][j] << "\n";
for(int h = 0; h <= 15; h ++)
{
if(r[h][a[i + 1]] == b[i + 1])
{
// cout << "MERGEM urm " << h << " cost " << cost[j][h] << "\n";
dp[i + 1][h] = min(dp[i + 1][h], dp[i][j] + cost[j][h]);
}
}
}
}
}
// cout << (int)a[n] << " " << (int)b[n] << " " << r[0][0] << "\n";
rez = sqrInf;
for(int i = 0; i <= 15; i ++)
{
if(r[i][a[n]] == b[n])
rez = min(rez, dp[n][i]);
}
}
void solve()
{
preCalc();
getCosts();
getDp();
}
void printFile()
{
cout << rez << "\n";
}
int main()
{
readFile();
solve();
printFile();
return 0;
}
