#include<stdio.h>
#include<vector>
#include<algorithm>

using namespace std;

#define lg 250005

vector<int> v[lg], vc[lg], cuoada[1005];
int n, m, np, nf, x, y, cst, i, j, k, nod, maxcost, nr[lg], nrp[1005];
int main()
{
	freopen("pscnv.in", "rt", stdin);
	freopen("pscnv.out", "wt", stdout);
	
	scanf("%d%d%d%d", &n, &m, &np, &nf);
	for (i = 1; i <= m; i ++){
		scanf("%d%d%d", &x, &y, &cst);
		
		nr[x] ++;
		v[x].push_back(y);
		vc[x].push_back(cst);
		
		maxcost = max(maxcost, cst);
	}
	
	nrp[0] = 1;
	cuoada[0].push_back(np);
	for (i = 0; i <= maxcost; i ++)
		for (j = 0; j < nrp[i]; j ++){
			x = cuoada[i][j];
			if (x == nf){
				printf("%d\n", i);
				return 0;
			}
			
			for (k = 0; k < nr[x]; k ++){
				nod = v[x][k];
				cst = vc[x][k];
				
				if (cst < i){
					nrp[i] ++;
					cuoada[i].push_back(nod);
				}
				else{
					nrp[cst] ++;
					cuoada[cst].push_back(nod);
				}
			}
		}
	
	return 69;
}