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

string a, b, c;
int n;

int main() {
  int ans = 0;
  cin >> n >> a >> b >> c;
  for(int i = 0; i < n; ++i) {
    if(a[i] == b[i] && b[i] == c[i])
      continue;
    else if(a[i] == b[i] || b[i] == c[i] || c[i] == a[i])
      ++ans;
    else
      ans += 2;
  }
  cout << ans << endl;
  return 0;
}