#include <bits/stdc++.h>
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]&&C[i]!=A[i]) ans+=2;
        else if(!(A[i]==B[i]&&B[i]==C[i])) ans++;
    }
    cout<<ans<<endl;
}
