#include <bits/stdc++.h>

#define FO(i,a,b) for (int i = (a); i < (b); i++)
#define sz(v) int(v.size())

using namespace std;

int n;
int d[105];

int main() {
    scanf("%d", &n);
    int l = 0;
    FO(i,0,n) {
        int x; scanf("%d", &x);
        d[x]++;
        l = max(l, x);
    }
    int mnr = l;
    FO(i,0,l+1) {
        int r = max(i, l-i);
        mnr = min(mnr, r);
        if (--d[r] < 0) {
            printf("Impossible\n");
            exit(0);
        }
    }
    for (int i = mnr; i >= 0; i--) if (d[i]) {
        printf("Impossible\n");
        exit(0);
    }
    printf("Possible\n");
}
