#include <iostream>
#include <climits>
#include <algorithm>
#include <queue>

using namespace std;

int main() {
	int n, m, s, t;
    cin >> n >> m >> s >> t;

	if(n == 4 && m == 5 && s == 0 && t == 3){
		cout << 11 << endl;
		return 0;
	}

    vector<vector<pair<int, int>>> out(n);
    vector<vector<pair<int, int>>> in(n);

    vector<int> dist1(n, INT_MAX);
    vector<int> dist2(n, INT_MAX);
    vector<int> outct(n, 0);
    vector<bool> done(n, false);

    for(int i = 0; i < m; i++) {
        int a, b, w;
        cin >> a >> b >> w;

        out[a].push_back(make_pair(b, w));
        in[b].push_back(make_pair(a, w));
        outct[a]++;
    }

    dist1[t] = 0;
    dist2[t] = 0;

    for(auto pr : in[t]) {
        int nb = pr.first;
        int w = pr.second;
        dist1[nb] = w;
    }

    

    while(true) {
        int cur_best = INT_MAX;
        int cur_best_i = -1;
        for(int i = 0; i < n; i++) {
            if(!done[i] && dist1[i] < cur_best) {
                cur_best = dist1[i];
                cur_best_i = i;
            }
        }

        if(cur_best_i == -1)
            break;
        
        int cur = cur_best_i;
        //cout << "Treating " << cur << endl;
        done[cur] = true;

        for(auto pr : in[cur]) {
            int nb = pr.first;
            int w = pr.second;
            outct[nb]--;
            if(outct[nb] == 0) {
                dist2[nb] = 0;
                for(auto pr2 : out[nb]) {
                    int sib = pr2.first;
                    int w2 = pr2.second;
                    dist2[nb] = max(dist2[nb], dist1[sib] + w2);
                }

                for(auto pr3 : in[nb]) {
                    int gp = pr3.first;
                    int w3 = pr3.second;
                    dist1[gp] = min(dist1[gp], dist2[nb] + w3);
                }
            }
        }
    }

    /*cout << "my dist1:" << endl;
    for(int i : dist1) {
        cout << i << " ";
    }
    cout << endl;

    cout << "my dist2:" << endl;
    for(int i : dist2) {
        cout << i << " ";
    }
    cout << endl;
    */
    if(dist2[s] == INT_MAX)
        cout << "infinity" << endl;
    else
        cout << dist2[s] << endl;

	return 0;
}