rt，WA on #11。

#include <bits/stdc++.h>
using namespace std;
const int maxn = 310;
#define ll long long
#define endl '\n'
ll g[maxn][maxn];
int n, m;

int main() {
	ios::sync_with_stdio(false);
	cin.tie(0), cout.tie(0);
	memset(g, 0x3f, sizeof(g));
	for (int i = 0; i <= 301; i++) {
	    g[i][i] = 0;
	}
	cin >> n >> m;
	for (int i = 1; i <= m; i++) {
		int u, v, w;
		cin >> u >> v >> w;
		g[u][v] = g[v][u] = w;
	}
	for (int k = 2; k <= n; k++) {
		for (int i = 2; i <= n; i++) {
			for (int j = 2; j <= n; j++) {
				g[i][j] = min(g[i][j], g[i][k] + g[k][j]);
			}
		}
	}
	ll ans = 0x3f3f3f3f3f3f3f3f;
	for (int i = 2; i <= n; i++) {
		for (int j = i + 1; j <= n; j++) {
			ans = min(ans, g[1][i] + g[i][j] + g[j][1]);
		}
	}
	if (ans == 0x3f3f3f3f3f3f3f3f) {
		ans = -1;
	}
	cout << ans << endl;
	return 0;
}