#include <iostream>
#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
ll n,ans;
string a,b,c;
int main(void){
    cin>>n>>a>>b>>c;
    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+=0;
        else ans+=1;
    }
    cout<<ans<<endl;
}
