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

int main() {
  int N, ans = 0;
  string A, B, C;
  cin >> N >> A >> B >> C; 
  for(int i = 0; i < N; i++) {
    if(A[i] != B[i] && B[i] != C[i] && A[i] != C[i]) ans+=2;
    else if(A[i] != B[i])ans++;
    else if(A[i] != C[i])ans++;
    else if(B[i] != C[i])ans++;
  }
  cout << ans;
}