#include <bits/stdc++.h>
using namespace std;
inline int read() {
  int n = 0, f = 1, ch = getchar();
  while (ch < '0' || ch > '9') {
    if (ch == '-') f = -1;
    ch = getchar();
  }
  while (ch >= '0' && ch <= '9') {
    n = n * 10 + ch - '0';
    ch = getchar();
  }
  return n * f;
}
char a[2000005], b[2000005];
int n;
int c[2000005];
int get(int x) {
  int cur = 0, res = 0;
  for (int i = 1; i <= n; i++) {
    cur += x * c[i];
    res = max(res, cur);
    if (cur < 0) cur = 0;
  }
  return res;
}
int main() {
  int s1 = 0, s2 = 0;
  n = read();
  scanf("%s%s", a + 1, b + 1);
  for (int i = 1; i <= n; i++) {
    if (a[i] != b[i] && a[i] == '0')
      c[i] = -1, s1++;
    else if (a[i] != b[i] && a[i] == '1')
      c[i] = 1, s2++;
  }
  if (s1 != s2) {
    printf("-1\n");
    return 0;
  }
  printf("%d\n", max(get(1), get(-1)));
  return 0;
}
