#include <bits/stdc++.h>
//#define int long long
using namespace std;

signed main()
{
	//ios::sync_with_stdio(false);
	int n,cnt=0;
	string a,b,c;
	cin>>n>>a>>b>>c;
	for(int i=0;i<n;i++){
		if(a[i]==b[i]&&b[i]==c[i]) continue;
		else if(a[i]==b[i]||b[i]==c[i]||a[i]==c[i]) cnt++;
		else cnt+=2;
	}
	cout<<cnt<<endl;
	return 0;
}