uva 11850

#include <iostream>
#include <cstdio>
#include <algorithm>
#include <cstring>
#include <string>
#include <cctype>
#include <stack>
#include <queue>
#include <list>
#include <vector>
#include <map>
#include <sstream>
#include <cmath>
#include <bitset>
#include <utility>
#include <set>
#include <numeric>
#define INT_MAX 2147483647
#define INT_MIN -2147483647
#define pi acos(-1.0)
#define N 1000000
#define LL unsigned long long
using namespace std;


int main ()
{
    int n;

    while ( scanf ("%d", &n) && n ) {
        int a [1422 + 10];

        for ( int i = 0; i < n; i++ ) scanf ("%d", &a [i]);

        sort (a, a + n);

        bool possible = true;

        for ( int i = 1; i < n; i++ )
            if ( a [i] - a [i - 1] > 200 ) possible = false;

        if ( 2 * (1422 - a [n - 1]) > 200 ) possible = false;

        if ( possible ) printf ("POSSIBLE\n");
        else printf ("IMPOSSIBLE\n");
    }

    return 0;
}