#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef double lf;
typedef long double Lf;
typedef pair <int,int> pii;
typedef pair <ll, ll> pll;
#define TRACE(x) cerr << #x << " " << x << endl
#define FOR(i, a, b) for (int i = (a); i < int(b); i++)
#define REP(i, n) FOR(i, 0, n)
#define all(x) (x).begin(), (x).end()
#define _ << " " <<
#define fi first
#define sec second
#define mp make_pair
#define pb push_back
const int MAXN = 2010;
int n;
char s[MAXN], p[MAXN];
int dp[MAXN];
int main() {
cin >> n;
cin >> s >> p;
REP(i, n) {
s[i] -= '0';
p[i] -= '0';
}
for (int i = n; i > 0; i--) {
s[i] = s[i - 1];
p[i] = p[i - 1];
}
FOR(i, 1, n + 1) {
bool sve1 = true, sve0 = true, ksor = true, isto = true;
dp[i] = (1 << 30);
for (int j = i; j > 0; j--) {
if (p[j]) sve0 = false;
if (!p[j]) sve1 = false;
if (p[j] == s[j]) ksor = false;
if (p[j] != s[j]) isto = false;
if (!sve0 && !sve1 && !ksor && !isto) break;
dp[i] = min(dp[i], dp[j - 1] + 1);
if (isto) dp[i] = min(dp[i], dp[j - 1]);
}
}
cout << dp[n] << endl;
return 0;
}
