#include<bits/stdc++.h>
using namespace std;
#define ll long long
int n,ans;
string a,b,c;
int main(){
    cin>>n>>a>>b>>c;
    ans=2*n;
    for(int i=0;i<n;i++){
        char x=a[i];
        char y=b[i];
        char z=c[i];
        if(x==y&&y==z)ans-=2;
        else if(x==y||x==z||y==z)ans--;
    }
    cout<<ans<<endl;
    return 0;
}