#include <bits/stdc++.h>
#define int long long
#define iostream() ios::sync_with_stdio(false),cin.tie(NULL),cout.tie(NULL);
#define elif(a) else if(a)
#define when(a) if (a)
#define tri() cout << "TRIANGLE\n"
#define seg() cout << "SEGMENT\n"
#define imp() cout << "IMPOSSIBLE\n"
using namespace std;
const int maxn = 1e6+7;
const int MAXN = maxn / 2;
signed main()
{
    iostream();
    int a,b,c,d;
    cin >> a >> b >> c >> d;
    when (a + b > c) tri();
    elif (a + b > d) tri();
    elif (a + c > b) tri();
    elif (a + c > d) tri();
    elif (a + d > b) tri();
    elif (a + d > c) tri();
    elif (b + c > a) tri();
    elif (b + c > d) tri();
    elif (b + d > a) tri();
    elif (b + d > c) tri();
    elif (c + d > a) tri();
    elif (c + d > b) tri();
    elif (a + b == c) seg();
    elif (a + b == d) seg();
    elif (a + c == b) seg();
    elif (a + c == d) seg();
    elif (a + d == b) seg();
    elif (a + d == c) seg();
    elif (b + c == a) seg();
    elif (b + c == d) seg();
    elif (b + d == a) seg();
    elif (b + d == c) seg();
    elif (c + d == a) seg();
    elif (c + d == b) seg();
    elif (a + b < c) imp();
    elif (a + b < d) imp();
    elif (a + c < b) imp();
    elif (a + c < d) imp();
    elif (a + d < b) imp();
    elif (a + d < c) imp();
    elif (b + c < a) imp();
    elif (b + c < d) imp();
    elif (b + d < a) imp();
    elif (b + d < c) imp();
    elif (c + d < a) imp();
    elif (c + d < b) imp();
    //暴力美学
 	return 0;
}