#include<bits/stdc++.h>

using namespace std;

#define x first
#define y second
#define pb push_back
#define eb emplace_back
#define rep(i,a,b) for(auto i = (a); i != (b); ++i)
#define REP(i,n) rep(i,0,n)
#define all(v) (v).begin(), (v).end()

typedef long long ll;
typedef long double ld;
typedef pair<int, int> ii;
typedef vector<int> vi;
typedef vector<vi> vvi;
typedef vector<ii> vii;

const int maxn = 1e5;
const int INF = 21e8;

int N, M, S, T, indeg[maxn + maxn] = {};
vii E[maxn + maxn];

int run()
{
	vi d(N + N, INF);
	REP(i, N) d[i + i] = -INF; // maximizes time

	priority_queue<ii> pq;
	pq.emplace(-(d[T + T] = 0), T + T); // max had turn, but finishes
	pq.emplace(-(d[T+1+T] = 0), T+1+T); // min had turn, but finishes

	while (!pq.empty()) {
		ii cur = pq.top();
		pq.pop();

		if (-cur.x != d[cur.y]) continue; // old edge
		if (cur.y == S + S) return -cur.x;

		if (cur.y & 1) {
			for (ii nxt : E[cur.y]) {
				int alt = nxt.y - cur.x;
				if (alt > d[nxt.x]) d[nxt.x] = alt;
				// last one to maximize over
				if (--indeg[nxt.x] == 0) pq.emplace(-d[nxt.x], nxt.x);
			}
		} else {
			for (ii nxt : E[cur.y]) {
				int alt = nxt.y - cur.x;
				// minimize version
				if (alt < d[nxt.x]) pq.emplace(-(d[nxt.x] = alt), nxt.x);
			}
		}
	}
	return INF;
}

int main()
{
	srand(time(NULL));

	ios_base::sync_with_stdio(false);
	cin.tie(NULL);
	cout.tie(NULL);

	cin >> N >> M >> S >> T;
	REP(i, M) {
		// consider reverse edges!
		int u, v, t;
		cin >> v >> u >> t;
		E[u + u].eb(v + v + 1, t); indeg[v+1+v]++;
		E[u + u + 1].eb(v + v, t); indeg[v + v]++;
	}

	int answer = run();
	if (answer == INF) cout << "infinity" << endl;
	else cout << answer << endl;

	return 0;
}