#include <iostream>
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]){
  if(b[i]!=c[i])ans++;
  }
    else if(b[i]==c[i])ans++;
    else if(a[i]==c[i])ans++;
    else ans+=2;
  }
  cout<<ans<<endl;
}