#include <bits/stdc++.h>
using namespace std;
char A[105], B[105], C[105];
int main(){
	int N; scanf("%d",&N);
	scanf("%s%s%s",A,B,C);
	int ans = 0;
	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] || C[i]==A[i]) ++ans;
		else ans += 2;
	}
	printf("%d\n",ans);
	return 0;
}