#include<iostream>
#include<algorithm>
using namespace std;
int main()
{
int n,i,a[1423],ok,aux,l;
while(cin>>n&&n)
{
for(i=1;i<=n;i++)
cin>>a[i];
sort(a,a+n);
ok=1;
if(1422-a[n]>100)
cout<<"IMPOSSIBLE\n";
else
{
for(i=0;i<n;i++)
if((a[i+1]-a[i])>200)
{
ok=0;
cout<<"IMPOSSIBLE\n";
break;
}
if(ok)
cout<<"POSSIBLE\n";
}
}
return 0;
}
fml still wa
srry for wasting so much of ur time 