#include <bit>
#include <bitset>
#include <assert.h>
#include <stdio.h>
#include <string.h>
#include <algorithm>
#include <sstream>
#include <iostream>
#include <set>
#include <map>
#include <vector>
#include <math.h>
#include <stdlib.h>
#include <queue>
#include <stack>


typedef long double ld;
typedef long long ll;

using namespace std;

string a, b, c;
int n;

int main() {
	cin >> n;
	cin >> a >> b >> c;
	int ret = 0;
	for (int i = 0; i < n; i++) {
		set<char> s;
		s.insert(a[i]);
		s.insert(b[i]);
		s.insert(c[i]);
		//cerr << s.size() << endl;
		ret += s.size() - 1;
	}
	cout << ret << endl;
	return 0;
}

#include <bits/stdc++.h>
#include <algorithm>
#include <cmath>
#include <cstdio>
#include <cstdlib>
#include <deque>
#include <functional>
#include <iostream>
#include <map>
#include <queue>
#include <set>
#include <stack>
#include <string>
#include <tuple>
#include <utility>
#include <vector>
#define pi 3.14159265358979323846264338327950L
using namespace std;

int main() {
  int N, ans;
  string A, B, C;
  cin >> N >> A >> B >> C;
  ans=0;
  for (int i=0; i<N; i++) {
    if (A[i]==B[i] && B[i]==C[i]) {
      ans=ans;
    }
    else {
      if (A[i]==B[i] || B[i]==C[i] || C[i]==A[i]) {
        ans=ans+1;
      }
      else {
        ans=ans+2;
      }
    }
  }
  cout << ans << endl;
}
