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#include <algorithm>
#include <iostream>
#include <tuple>
#include <vector>
constexpr long long inf = 999999999999999LL;
size_t findcycle(
size_t v,
const std::vector<std::tuple<size_t, size_t, long long>>& a,
const std::vector<size_t>& p
) {
std::vector<bool> visited(p.size(), false);
visited[v] = true;
size_t u = p[v];
while (!visited[u]) {
visited[u] = true;
u = p[u];
}
return u;
}
int main() {
size_t n, m;
std::cin >> n >> m;
std::vector<std::tuple<size_t, size_t, long long>> a(m);
for (size_t i = 0; i < m; i++) {
size_t x, y;
long long w;
std::cin >> x >> y >> w;
a[i] = {x-1, y-1, w};
}
std::vector<size_t> p(n, n);
std::vector<long long> d(n, -inf);
d[0] = 0;
std::vector<bool> reach_1(n, false), reach_n(n, false);
reach_1[0] = reach_n[n-1] = true;
for (size_t i = 0; i < n; i++) {
for (auto [v, u, w] : a) {
if (d[u] < d[v] + w) {
d[u] = d[v] + w;
p[u] = v;
}
reach_n[v] = reach_n[v] || reach_n[u];
reach_1[u] = reach_1[u] || reach_1[v];
}
}
for (auto [v, u, w] : a) {
if (d[u] < d[v] + w) {
size_t x = findcycle(u, a, p);
if (reach_1[x] && reach_n[x]) {
std::cout << "-1\n";
return 0;
}
}
}
std::cout << d[n-1] << "\n";
}
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