#include"testlib.h"
#include<bits/stdc++.h>
using namespace std;
using ll = long long;

const ll Nmin = 2, Nmax = 200'000;

int main(){
    registerValidation();
    ll N = inf.readLong(Nmin, Nmax);
    inf.readEoln();
    vector<ll> P(N);
    for (ll i = 1; i <= N; i++){
        if (i != 1){
            inf.readSpace();
        }
        P[i-1] = inf.readLong(1LL, N);
    }
    inf.readEoln();
    ranges::sort(P);
    for (ll i = 1; i <= N; i++){
        inf.ensuref(P[i-1] == i, "P is permutation");
    }

    inf.readEof();
    return 0;
}