91WA，求教

#include<bits/stdc++.h>
using namespace std;
const int N = 1515;
long long n, m, a, b;
vector<pair<long long,long long>> g[N];
long long ans = -1;
long long d[N];
void dfs(long long x, long long len) {
	if(x == n) { ans = max(ans, len); return; }
	if(d[x] > len) return;
	d[x] = len;
	for(long long i=0; i<g[x].size(); i++) {
		long long y = g[x][i].first, z = g[x][i].second;
		dfs(y, len+z);
	}
}
int main() {
	cin >> n >> m;
	while(m--) {
		long long x, y, z;
		scanf("%lld%lld%lld", &x, &y, &z);
		g[x].push_back({y,z});
	}
	dfs(1, 0);
	cout << ans << endl;
	return 0;
}