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

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;
    else if(a[i] == b[i] || b[i] == c[i] || c[i] == a[i]) ans++;
    else ans += 2;
  }

  cout << ans << endl;
}