#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using ld = long double;
using vl = vector<ll>;
using vll = vector<vl>;
using Pll = pair<ll, ll>;
#define rep(i,n) for(ll i=0;i<(ll)(n);i++)
#define all(v) v.begin(), v.end()
#define sz(x) ((int) x.size())
#define pb push_back
#define mp make_pair
#define mt make_tuple
#define F first
#define S second
const int MOD = 1e9+7;
const int INF = 2e9;
template<class T> void print(const T& t){ cout << t << endl; }
template<class T> inline bool chmax(T& a, T b) { if (a < b) { a = b; return 1; } return 0; }
template<class T> inline bool chmin(T& a, T b) { if (a > b) { a = b; return 1; } return 0; }
int gcd(int a,int b){return b?gcd(b,a%b):a;}

int main(){
  ll n;
  cin >> n;
  string a, b, c;
  cin >> a >> b >> c;
  ll ans = 0;
  rep(i,n){
    if(a[i]==b[i]&&b[i]==c[i]){
      continue;
    }
    else if(a[i]!=b[i]&&b[i]!=c[i]&&c[i]!=a[i]){
      ans += 2;
    }
    else{
      ans++;
    }
  }
  print(ans);
}
#define rep(i,n) for(ll i=0, i##_len=(n); i<i##_len; ++i)
#define rrep(i,a,b) for(ll i=(b)-1; i>=a; --i)
#define repi(i,a,b) for(ll i=ll(a);i<ll(b);++i)
#define ALL(obj) (obj).begin(), (obj).end()
#define scanv(n,v) v.resize(n); rep(i,n){ cin>>v[i];}
#define MOD 1000000007ll
#define Yes(flag) cout<<((flag)? "Yes":"No");
#define YES(flag) cout<<((flag)? "YES":"NO");
#define be begin
#define pb push_back
#define fi first
#define se second
#define square(x) x*x
#include<bits/stdc++.h>
using ll = long long;
using namespace std;
template<class T>T 
chmin(T& a,T b){if(a>b){a=b;return true;}return false;}
template<class T>T 
chmax(T& a,T b){if(a<b){a=b;return true;}return false;}
//------------------------------------------------------
int eq(char a,char b,char c){
    vector<char> k{a,b,c};
    sort(ALL(k));
    return distance(k.begin(),unique(ALL(k)))-1;
}

int n;
string a,b,c;
void input(){
    cin>>n>>a>>b>>c;
}
void src(){
    int ans=0;
    rep(i,n){
        ans+=eq(a[i],b[i],c[i]);
    }
    cout<<ans;
}    
int main(int argc,char* argv[]){
    ios::sync_with_stdio(false);
   // ifstream in( argv[1] ); cin.rdbuf(in.rdbuf());
    input();
    src();    
}