#include <bits/stdc++.h>
using namespace std;
int n,ans,b[110],a[110][30];
char c;
int main()
{
  cin>>n;
  for(int t=0;t<3;++t)
  for(int i=0;i<n;++i) cin>>c,
   	  				   a[i][c-'a']++,
    				   b[i]=max(b[i],a[i][c-'a']);
  for(int i=0;i<n;++i) ans+=3-b[i];
  cout<<ans;
}
