#include <bits/stdc++.h>
using namespace std;
template<typename T>
void out(T x) { cout << x << endl; exit(0); }
#define watch(x) cout << (#x) << " is " << (x) << endl
using ll = long long;
const int maxn = 1e6 + 5;
int n;
int dp[1<<19];
int convert(string a) {
int tmp = 0;
for (char c: a) {
tmp *= 2;
tmp += (c-'0');
}
return tmp;
}
int main() {
ios_base::sync_with_stdio(false); cin.tie(0); cout.tie(0);
cin>>n;
string a, b;
cin>>a;
cin>>b;
int start = convert(a);
for (int i=0; i<1<<n; i++) {
dp[i] = 1e9;
}
dp[start] = 0;
queue<int> qq;
qq.push(start);
auto flip = [&](int mask, int l, int r) {
int cover = (1<<(r-l+1)) - 1;
cover <<= l;
return mask^cover;
};
auto one = [&](int mask, int l, int r) {
int cover = (1<<(r-l+1)) - 1;
cover <<= l;
return mask|cover;
};
auto zero = [&](int mask, int l, int r) {
int cover = (1<<(r-l+1)) - 1;
cover <<= l;
return mask&(~cover);
};
while (qq.size()) {
int mask = qq.front();
qq.pop();
for (int l=0; l<n; l++) {
for (int r=l; r<n; r++) {
for (int nmask: {flip(mask,l,r), one(mask,l,r), zero(mask,l,r)}) {
if (dp[nmask]>1+dp[mask]) {
dp[nmask] = 1+dp[mask];
qq.push(nmask);
}
}
}
}
}
cout<<dp[convert(b)]<<endl;
return 0;
}
