#include <bits/stdc++.h>
using namespace std;
int a[4];
int main() {
  for (int i = 0; i < 4; i++) cin >> a[i];
  sort(a, a + 4);
  if (a[0] + a[1] > a[2] || a[1] + a[2] > a[3])
    cout << "TRIANGLE\n";
  else if (a[0] + a[1] == a[2] || a[1] + a[2] == a[3])
    cout << "SEGMENT\n";
  else
    cout << "IMPOSSIBLE\n";
  return 0;
}
