#include <bits/stdc++.h>
using namespace std;
int main() {
  int a[5], i, j;
  for (i = 0; i < 4; i++) {
    cin >> a[i];
  }
  sort(a, a + 4);
  if (a[0] + a[1] > a[2] || a[2] + a[1] > a[3])
    cout << "TRIANGLE" << endl;
  else if (a[0] + a[1] == a[2] || a[2] + a[1] == a[3])
    cout << "SEGMENT" << endl;
  else
    cout << "IMPOSSIBLE" << endl;
}
