#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <vector>
#include <algorithm>
#include <cctype>
using namespace std;

const int NMAX = 250005, INF = 0x3f3f3f3f, MAXB = 8192;

int N, M, Start, End, X, Y, C, Ans[NMAX], Ptr;
vector<pair<int, int> > G[NMAX];
vector<int> List[1010];
char Buf[MAXB];

int GetAns()
{
    memset(Ans, INF, sizeof(Ans));
    Ans[Start] = 0;
    List[0].push_back(Start);
    for(int i = 0; i <= 1000; ++ i)
        for(size_t j = 0; j < List[i].size(); ++ j)
        {
            int Node = List[i][j];

            if(Node == End) return i;
            if(Ans[Node] != i) continue;

            for(size_t k = 0; k < G[Node].size(); ++ k)
            {
                int NowCost = max(Ans[Node], G[Node][k].second);
                if(NowCost >= Ans[ G[Node][k].first ]) continue;
                Ans[ G[Node][k].first ] = NowCost;
                List[NowCost].push_back( G[Node][k].first );
            }
        }
}

int GetInt()
{
    int Ans = 0;
    while(!isdigit(Buf[Ptr]))
        if(++ Ptr >= MAXB)
            fread(Buf, 1, MAXB, stdin), Ptr = 0;
    while(isdigit(Buf[Ptr]))
    {
        Ans = Ans * 10 + Buf[Ptr] - '0';
        if(++ Ptr >= MAXB)
            fread(Buf, 1, MAXB, stdin), Ptr = 0;
    }

    return Ans;
}

int main()
{
    freopen("pscnv.in", "r", stdin);
    freopen("pscnv.out", "w", stdout);
    fread(Buf, 1, MAXB, stdin);

    N = GetInt();
    M = GetInt();
    Start = GetInt();
    End = GetInt();
    for(int i = 1; i <= M; ++ i)
    {
        X = GetInt();
        Y = GetInt();
        C = GetInt();
        G[X].push_back(make_pair(Y, C));
        G[Y].push_back(make_pair(X, C));
    }

    printf("%i\n", GetAns());
    return 0;
}