#include <bits/stdc++.h>

using namespace std;

vector<string>s;
int n;
int mx[26];
vector < bool> del;
void no() {
    puts("NO");
    exit(0);
}
int main() {
#ifndef ONLINE_JUDGE
    freopen("data.in", "r", stdin);
#endif // ONLINE_JUDGE

    cin >> n;
    s.resize(n);
    del.resize(n);
    for(int i = 0; i < n; ++i) {
        cin >> s[i];
        vector<int>ap(26);

        for(auto it : s[i]) {
            ++ap[it - 'a'];

            if(ap[it - 'a'] > 1)no();
        }
    }
}