import java.util.*;
import java.lang.*;
import java.io.*;
class Main
{
private static class Node {
private int x;
private int y;
private int t;
private Node(int x, int y, int t) {
this.x = x;
this.y = y;
this.t = t;
}
}
{
Scanner in
= new Scanner
(System.
in); int n = in.nextInt();
int m = in.nextInt();
Node r = null;
Node[] canals = new Node[m + 1];
for (int i = 0; i < m; i++) {
int x = in.nextInt();
int y = in.nextInt();
int t = in.nextInt();
r = new Node(x, y, t);
canals[i] = r;
}
int INF = 2000000;
int[] distance = new int[n + 1];
int subs = -1;
for (int i = 0; i < n; i++) {
subs = -1;
for (int j = 0; j < m; j++) {
if (distance[canals[j].y] > distance[canals[j].x] + canals[j].t) {
distance
[canals
[j
].
y] = Math.
max (-INF, distance
[canals
[j
].
x] + canals
[j
].
t); subs = canals[j].y;
}
}
}
if (subs == -1) {
System.
out.
println("not possible"); }
else {
System.
out.
println("possible"); }
}
}
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