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

int N;
char A[110], B[110], C[110];

int main(){
	scanf("%d%s%s%s",&N, A, B, C);
	int ret = 0;

	for(int i=0;i<N;++i){
		char a = A[i], b = B[i], c = C[i];
		if(a == b && b == c && c == a) ret+=0;
		else if (a == b || b == c || c == a) ret+=1;
		else ret+=2;
	}
	printf("%d\n",ret);
	return 0;
}
