#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 maxm = 2e5;

const int INF = 2e9;

int N, M, S, T;

struct edge { int fr, to, time; };

edge g[maxm];
// ub: the   latest time the maximize half can achieve
// lb: the earliest time the minimize half can achieve
int ub[maxn], lb[maxn];
// pu: previous maximum
// pl previous minimum
int pu[maxn], pl[maxn];

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

	cin >> N >> M >> S >> T;
	REP(i, M) cin >> g[i].fr >> g[i].to >> g[i].time;

	fill_n(ub, N, -INF);
	fill_n(lb, N, INF);

	ub[T] = 0; // starting point.
	lb[T] = 0;
	bool done;

	int nupdates_sub = 0;

	do {
		done = true;
		REP(idx, M) {
			int j = g[idx].fr;
			int i = g[idx].to;
			int t = g[idx].time;
			// try i -> j (time t)
			if (lb[i] != INF && (lb[i] + t > ub[j] || (pu[j] == i && lb[i] + t != ub[j]))) {
				int old_time = ub[j];
				ub[j] = lb[i] + t;

				if (j == S && ub[j] > old_time && ++nupdates_sub > N) {
					// increased more than once:
					// cerr << "NEW TIME: " << old_time << " -> " << ub[j] << endl;
					cout << "infinity" << endl;
					exit(0);
				}

				pu[j] = i;
				done = false;
			}
			if (ub[i] != -INF && (ub[i] + t < lb[j] || (pl[j] == i && ub[i] + t != lb[j]))) {
				lb[j] = ub[i] + t;
				pl[j] = i;
				done = false;
			}
		}
	} while (!done);

	REP(i, N) cerr << lb[i] << " " << ub[i] << endl;
	// cout << lb[S] << " " << ub[S] << endl;
	cout << ub[S] << endl;
	// cerr << endl;

	return 0;
}