Problem:
Score : 400 points

Problem Statement

There is a directed graph with N vertices and M edges.
The i-th edge (1≤i≤M) points from vertex a_i to vertex b_i, and has a weight c_i.
We will play the following single-player game using this graph and a piece.

Initially, the piece is placed at vertex 1, and the score of the player is set to 0.
The player can move the piece as follows:

When the piece is placed at vertex a_i, move the piece along the i-th edge to vertex b_i. After this move, the score of the player is increased by c_i.

The player can end the game only when the piece is placed at vertex N.
The given graph guarantees that it is possible to traverse from vertex 1 to vertex N.

When the player acts optimally to maximize the score at the end of the game, what will the score be?
If it is possible to increase the score indefinitely, print inf.

Constraints

2≤N≤1000

1≤M≤min(N(N-1),2000)

1≤a_i,b_i≤N (1≤i≤M)

a_i≠b_i (1≤i≤M)

a_i≠a_j or b_i≠b_j (1≤i<j≤M)

-10^9≤c_i≤10^9 (1≤i≤M)

c_i is an integer.

In the given graph, there exists a path from vertex 1 to vertex N.

Input

Input is given from Standard Input in the following format:

N M
a_1 b_1 c_1
a_2 b_2 c_2
:
a_M b_M c_M

Output

Print the maximum possible score at the end of the game, if it is finite. If it is possible to increase the score indefinitely, print inf.

Sample Input 1

3 3
1 2 4
2 3 3
1 3 5

Sample Output 1

7

There are two ways to move the piece to vertex N=3:

vertex 1 → vertex 2 → vertex 3 : score 4+3=7

vertex 1 → vertex 3 : score 5

Thus, the maximum possible score at the end of the game is 7.

Sample Input 2

2 2
1 2 1
2 1 1

Sample Output 2

inf

It is possible to increase the score indefinitely by alternating between vertex 1 and 2.

Sample Input 3

6 5
1 2 -1000000000
2 3 -1000000000
3 4 -1000000000
4 5 -1000000000
5 6 -1000000000

Sample Output 3

-5000000000

Solution in C++14 (GCC 5.4.1) (judge verdict: Wrong Answer)

#include <bits/stdc++.h>
using namespace std;

// iterator
#define REP(i,init, n) for(lli i=init;i<n;i++)
#define REPE(i,init, n) for(lli i=init;i<=n;i++)
#define REPIT(it,container) for(auto it = container.begin(); it != container.end(); it++)
#define REPIT_R(it,container) for(auto it = container.rbegin(); it != container.rend(); it++)

// input
#define cin1(x)             cin >> x
#define cin2(x, y)          cin >> x >> y
#define cin3(x, y, z)       cin >> x >> y >> z
#define ncin1(n, x)         REP(i, 0, n) {cin1(x[i]);}
#define ncin2(n, x, y)      REP(i, 0, n) {cin2(x[i], y[i]);}
#define ncin3(n, x, y, z)   REP(i, 0, n) {cin3(x[i], y[i], z[i]);}

#define ARRAY_LENGTH(array) (sizeof(array) / sizeof(array[0]))

typedef long long int lli;
typedef pair<lli, lli> P;

struct edge {
    lli from;
    lli to;
    lli cost;
};
vector<edge> edges;


lli d[1001]; // 各頂点の始点からの距離
lli V;       // 頂点の数
lli E;       // 辺の数
lli r;       // 始点の番号

bool calc_shortest_path(lli start) {
    REP(i, 0, V) {
        d[i] = LLONG_MAX;
    }
    d[start] = 0;

    lli loop_count = 0;
    bool updated;
    // O(V*E)
    while (true) {
        // V-1 回に収まっていなかったら、負の閉路がある
        // なぜなら、1 ループごとに少なくとも 1 つの最短経路が求まるから
        // V 個の頂点のうち、1 つは始点なので、V-1 個の最短経路が求まれば良い。
        if (loop_count == V)
            return false;

        updated = false;
        REP(i, 0, (lli)edges.size()) {
            edge e = edges[i];
            if (d[e.from] == LLONG_MAX)
                continue;
            if (d[e.from] + e.cost < d[e.to]) {
                d[e.to] = d[e.from] + e.cost;
                updated = true;
            }
        }

        loop_count++;
        if (!updated)
            break;
    }
    return true;
}
int main() {
    cin2(V, E);
    r = 1;
    REP(i, 0, E) {
        lli a, b, c;
        cin3(a, b, c);
        edge e = {a, b, -c};
        edges.push_back(e);
    }

    REPE(i, 1, V) {
        d[i] = LLONG_MAX/3;
    }
    d[1] = 0;
    if (calc_shortest_path(1)) {
        if (d[V] == LLONG_MAX)
            cout << "inf" << endl;
        else
            cout << -d[V] << endl;
    }
    else {
        cout << "inf" << endl;
    }

}