buckets.cpp

// NOTE: it is recommended to use this even if you don't understand the following code.

#include <iostream>
#include <fstream>
#include <vector>
#include <algorithm>

using namespace std;

// input data
long long N, i;
vector<long long> D;

int main() {
//  uncomment the following lines if you want to read/write from files
	ifstream cin("input.txt");
	ofstream cout("output.txt");

    cin >> N;
    D.resize(N);
    for (long long i=0; i<N; i++)
        cin >> D[i];

    // insert your code here
    bool ok = true;
    
    sort(D.begin(), D.end());
    
    for (long long i=1; i<N; i++) {
    	if (D[i] == D[i-1]) {
    		ok = false;
		}
	}

    cout << (ok ? "Ok" : "Impossible") << endl; // print the result
    return 0;
}