#include <cstring>
#include <cassert>
#include <vector>
#include <list>
#include <queue>
#include <map>
#include <set>
#include <deque>
#include <stack>
#include <bitset>
#include <algorithm>
#include <functional>
#include <numeric>
#include <utility>
#include <sstream>
#include <iostream>
#include <iomanip>
#include <cstdio>
#include <cmath>
#include <cstdlib>
#include <ctime>
#include <fstream>
#include <climits>
#define scan(a) scanf("%d",&a);
#define s2(a,b) scanf("%d %d",&a,&b)
#define PI 2acos(-1.0)
#define s1(a) scanf("%d",&a);
#define INF 2<<15
#define PB(A) push_back(A)
#define clr(a,b) memset(a,b,sizeof(a))
using namespace std;
int main()
{
int i,j,k;
int n;
int dis[1450];
while(cin>>n && n)
{
dis[0]=0;
for(i=1; i<=n; i++)
{
scanf("%d",&dis[i]);
}
sort(dis,dis+(n+1));
dis[n+1]=1422;
bool c=true;
for(i=1; i<=n; i++)
{
if((dis[i]-dis[i-1])>200)
{
c=false;
break;
}
}
if(dis[n+1]-dis[n]>100)
c=false;
if(c)
printf("POSSIBLE\n");
else
printf("IMPOSSIBLE\n");
}
}
#include <cassert>
#include <vector>
#include <list>
#include <queue>
#include <map>
#include <set>
#include <deque>
#include <stack>
#include <bitset>
#include <algorithm>
#include <functional>
#include <numeric>
#include <utility>
#include <sstream>
#include <iostream>
#include <iomanip>
#include <cstdio>
#include <cmath>
#include <cstdlib>
#include <ctime>
#include <fstream>
#include <climits>
#define scan(a) scanf("%d",&a);
#define s2(a,b) scanf("%d %d",&a,&b)
#define PI 2acos(-1.0)
#define s1(a) scanf("%d",&a);
#define INF 2<<15
#define PB(A) push_back(A)
#define clr(a,b) memset(a,b,sizeof(a))
using namespace std;
int main()
{
int i,j,k;
int n;
int dis[1450];
while(cin>>n && n)
{
dis[0]=0;
for(i=1; i<=n; i++)
{
scanf("%d",&dis[i]);
}
sort(dis,dis+(n+1));
dis[n+1]=1422;
bool c=true;
for(i=1; i<=n; i++)
{
if((dis[i]-dis[i-1])>200)
{
c=false;
break;
}
}
if(dis[n+1]-dis[n]>100)
c=false;
if(c)
printf("POSSIBLE\n");
else
printf("IMPOSSIBLE\n");
}
}