#ifdef Home
#define _GLIBCXX_DEBUG
#endif // Home
#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef long double ld;
const int N = 2022;
string a, b;
int dp[N][N][4];
// 0 don't touched
// 1 turn off all
// 2 turn on all
// 3 toggle all
int change(int pr, int cr) {
if(!cr) {
return pr;
}
if(cr < 3) {
return cr;
}
if(!pr) {
return cr;
}
if(pr < 3) {
return 3 - pr;
}
return 0;
}
int recur(int l, int r, int sts) {
int &ans = dp[l][r][sts];
if(ans != -1) {
return ans;
}
if(l + 1 == r) {
if(sts == 0) {
return ans = (a[l] != b[l]);
}
if(sts == 1) {
return ans = ('0' != b[l]);
}
if(sts == 2) {
return ans = ('1' != b[l]);
}
return ans = (a[l] == b[l]);
}
ans = r - l;
for(int m = l + 1; m < r; ++ m) {
int ansl = recur(l, m, sts);
for(int nwsts = 1; nwsts < 4; ++ nwsts) {
ansl = min(ansl, recur(l, m, change(sts, nwsts)) + 1);
}
int ansr = recur(m, r, sts);
for(int nwsts = 1; nwsts < 4; ++ nwsts) {
ansr = min(ansr, recur(m, r, change(sts, nwsts)) + 1);
}
ans = min(ans, ansl + ansr);
}
return ans;
}
main() {
#ifdef Home
freopen("input.txt", "r", stdin);
freopen("output.txt", "w", stdout);
#endif // Home
ios_base::sync_with_stdio(0);
cin.tie(0);
memset(dp, -1, sizeof dp);
int n;
cin >> n >> a >> b;
cout << min( {
recur(0, n, 0),
recur(0, n, 1) + 1,
recur(0, n, 2) + 1,
recur(0, n, 3) + 1} );
}
