#include<bits/stdc++.h>
int n,i,ans;
char c[3][105];
int main(){
	scanf("%d%s%s%s",&n,c[0]+1,c[1]+1,c[2]+1);
	for(i=1;i<=n;++i)
		ans+=c[0][i]==c[1][i]?(c[0][i]==c[2][i]?0:1):(c[2][i]==c[0][i] || c[2][i]==c[1][i]
			?1:2);
	printf("%d\n",ans);
	return 0;
}