#include<bits/stdc++.h> using namespace std; using ll = long long; using pll = pair<ll, ll>; #define drep(i, cc, n) for (ll i = (cc); i <= (n); ++i) #define rep(i, n) drep(i, 0, n - 1) #define all(a) (a).begin(), (a).end() #define pb push_back #define fi first #define se second mt19937_64 rng(chrono::system_clock::now().time_since_epoch().count()); const ll MOD1000000007 = 1000000007; const ll MOD998244353 = 998244353; const ll MOD[3] = {999727999, 1070777777, 1000000007}; const ll LINF = 1LL << 60LL; const int IINF = (1 << 30) - 1; void solve(){ int n; cin >> n; vector<string> s(n); for(int i=0; i<n; i++) cin >> s[i]; map<string, int> mp; for(int i=0; i<n; i++){ for(int j=0; j<26; j++){ string t = s[i] + (char)('a' + j); sort(all(t)); mp[t]++; } } for(auto [t, cnt] : mp){ if(cnt == 1){ cout << t << '\n'; return; } } cout << -1 << '\n'; } int main(){ cin.tie(nullptr); ios::sync_with_stdio(false); int T=1; //cin >> T; while(T--) solve(); }