#include<bits/stdc++.h>
using namespace std;
#define rep(i,n) for(int i = 0; i < (n); ++i)

int main(void)
{
    int n, cnt=0;
    string a,b,c;
    cin >> n >> a >> b >> c;
    rep(i,n) cnt += set<char>({a[i], b[i], c[i]}).size() - 1;
    cout << cnt << endl;
    return 0;
}
#include<bits/stdc++.h>
using namespace std;
#define rep(i,j,n) for(int i=(int)(j);i<(int)(n);i++)
#define REP(i,j,n) for(int i=(int)(j);i<=(int)(n);i++)
#define MOD 1000000007
#define int long long
#define ALL(a) (a).begin(),(a).end()
#define vi vector<int>
#define vii vector<vi>
#define pii pair<int,int>
#define priq priority_queue<int>
#define disup(A,key) distance(A.begin(),upper_bound(ALL(A),(int)(key)))
#define dislow(A,key) distance(A.begin(),lower_bound(ALL(A),(int)(key)))
#define tii tuple<int,int,int>
#define Priq priority_queue<int,vi,greater<int>>
#define pb push_back
#define mp make_pair
signed main(){
  int N; cin>>N;
  vector<string> S(3);
  rep(i,0,3) cin>>S[i];
  int ans=0;
  rep(i,0,N){
    set<char> T;
    rep(j,0,3)
      T.insert(S[j][i]);
    ans+=T.size()-1;
  }
  cout<<ans<<endl;
  }
