#include <vector>
#include <cstdio>
#include <iostream>
#include <algorithm>
#include <cmath>
#include <utility>
#include <cstdlib>

using namespace std;

#define MAX 10001

int inside[MAX], outside[MAX], changes[MAX];

void main( void )
{
  int n, m, x, k = 0;

  cin >> n >> m;

  for (int i = 0; i < m; i++)
  {
    cin >> inside[i] >> outside[i] >> changes[i];
    inside[i]--;
    outside[i]--;
  }

  vector<int> L(n, INT_MIN), p(n, -1), way;

  L[0] = 0;

  for (int i = 0; i < n; i++)
  {
    x = -1;
    for (int j = 0; j < m; j++)
      if (L[inside[j]] > INT_MIN &&
        L[outside[j]] < L[inside[j]] + changes[j])
      {
        L[outside[j]] = L[inside[j]] + changes[j];
        p[outside[j]] = inside[j];
        x = 1;
      }
  }

  for (int i = n - 1; i != -1; i = p[i])
  {
    k++;
    way.push_back(i);

    if (k > n)
      break;
  }

  if (L[n - 1] == INT_MIN)
    cout << ":(" << endl;

  else if (x != -1 && (way.back() !=0 || way.front() != n - 1 || k > n))
    cout << ":)" << endl;

  else
    cout << L[n - 1] << endl;
}