#include <iostream>
#include <algorithm>
using namespace std;

int main() {
	int n,count=0,co;
	char a[101], b[101], c[101];
	cin >> n >> a >> b >> c;
	for (int i = 0; i < n; i++) {
		co = 0;
		if (a[i] != b[i])co++;
		if (a[i] != c[i])co++;
		if (b[i] != c[i])co++;
		if(co != 0)count += co - 1;
	}
	cout << count << endl;
	return(0);
}