#include <bits/stdc++.h>
#define ll long long
#define ull unsigned long long
#define all(x) x.begin(), x.end()
#define Neco "lamps"
#define resp(x) sort(all(x)), x.resize(unique(all(x)) - x.begin())
#define getbit(x,i) ((x >> i)&1)
#define _left id * 2, l, mid
#define _right id * 2 + 1, mid + 1, r
#define cntbit(x) __builtin_popcountll(x)
#define fi(i, a, b) for(int i = a; i <= b; i++)
#define fid(i, a, b) for(int i = a; i >= b; i--)
#define maxn (int) 2e3 + 7
using namespace std;
const ll mod = 1e9 + 7; //972663749
const ll base = 911382323;
mt19937_64 rng(chrono::steady_clock::now().time_since_epoch().count());
ll GetRandom(ll l, ll r)
{
return uniform_int_distribution<ll> (l, r)(rng);
}
int n;
string a, b;
int dp[maxn][maxn][5];
char _get(char x, int type) {
if(type == 0) return x;
if(type == 1) return '0';
if(type == 2) return '1';
if(type == 3) return x == '0' ? '1' : '0';
}
int turn(int x, int t) {
if(x == 0) return t;
if(t == 0) return x;
if(t == 1) return min(2, x);
if(t == 2) return x == 2 ? 2 : 1;
if(t == 3) return x == 3 ? 0 : x;
}
int calc(int l, int r, int t)
{
if(l == r) return _get(a[l], t) == b[l] ? 0 : 1e9;
if(dp[l][r][t] >= 0) return dp[l][r][t];
int res = 1e9;
fi(i, l, r - 1) {
fi(x, 0, 3) fi(y, 0, 3)
{
int w, u = turn(x, t), v = turn(y, t);
if(x != y) w = (u != t) + (v != t);
else w = (u != t);
res = min(res, calc(l, i, u) + calc(i + 1, r, v) + w);
}
}
return dp[l][r][t] = res;
}
void solve()
{
cin >> n >> a >> b;
a = ' ' + a, b = ' ' + b;
memset(dp, -1, sizeof dp);
int res = 1e9;
fi(i, 0, 3) res = min(res, calc(1, n, i) + (i > 0));
cout << res;
// cout << calc(1, 1, 0);//get(a[1], 0);
}
int main()
{
ios_base::sync_with_stdio(0);
cin.tie(0);
cout.tie(0);
if(fopen(Neco".inp", "r")) {
freopen(Neco".inp", "r", stdin);
freopen(Neco".out", "w", stdout);
}
int nTest = 1;
// cin >> nTest;
while(nTest--)
{
solve();
}
return 0;
}
