#include <bits/stdc++.h>
typedef long long LL;
using namespace std;

int main(){
  int n; cin >> n;
  string a, b, c;
  cin >> a >> b >> c;

  int ans = 0;
  for (int i = 0; i < n; i ++) {
    if (a[i] == b[i] && b[i] == c[i]) continue;
    if (a[i] != b[i] && a[i] != c[i] && b[i] != c[i]) ans += 2;
    else ans ++;
  }

  cout << ans << endl;
}