#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef pair<ll,ll> pll;

int main() {
  ll n;
  cin >> n;
  vector<string> s(3);
  for(ll i=0;i<3;i++) {
    cin >> s[i];
  }
  ll ans=0;
  for(ll i=0;i<n;i++) {
    set<char> ss;
    for(ll j=0;j<3;j++) {
      ss.insert(s[j][i]);
    }
    ans+=ss.size()-1;
  }
  cout << ans << endl;
}
#include <bits/stdc++.h>
#define rep(i,n) for (int i = 0; i < (int)(n); i++)
#define REP(i,n) for (int i = 1; i < (int)(n); i++)
#define all(x) x.begin(),x.end()
#define rall(x) x.rbegin(),x.rend()
#define debug(var) do{cout << #var << " : "; view(var);}while(0)
template<class T> bool chmin(T &a, T b) {if(a>b) {a=b;return 1;}return 0;}
template<class T> bool chmax(T &a, T b) {if(a<b) {a=b;return 1;}return 0;}
using namespace std;
template<class T> void view(T e) {cout << e << endl;}
template<class T> void view(const vector<T> &v) {for(const auto &e : v){cout << e << " ";} cout << endl;}
template<class T> void view(const vector<vector<T>> &vv) {for(const auto &v : vv){view(v);}}
using vint = vector<int>;
using vvint = vector<vector<int>>;
using ll = long long;
using vll = vector<ll>;
using vvll = vector<vector<ll>>;
using P = pair<int,int>;
const int inf = 1e9;
const ll inf_l = 1e18;
const int MAX = 1e5;

int main() {
    int n; cin >> n;
    string a, b, c; cin >> a >> b >> c;
    int ans = 0;
    rep(i,n) {
        set<char> st;
        for (string s : vector<string>{a,b,c}) {
            st.insert(s[i]);
        }
        if (st.size() == 2) ans += 1;
        if (st.size() == 3) ans += 2;
    }
    cout << ans << endl;
}