#include <bits/stdc++.h>
using namespace std;
ifstream fin("sate.in");
ofstream fout("sate.out");
int n, m, x, y, dist[10005], viz[10005];
vector<pair<int, int>> mat[305];

void bfs(int x)
{
    int nodcrt;
    queue<int>q;
    q.push(x);
    viz[x]=1;
    dist[x]=0;
    while(!q.empty())
    {
        for(auto i:mat[nodcrt])
            if(viz[i.first]==0)
        {
            viz[i.first]=1;
            if(i.first>nodcrt)
                dist[i.first]=dist[nodcrt]+i.second;
            else
                dist[i.first]=dist[nodcrt]-i.second;
        }
    }
}

int main()
{
    int x,y,c;
    while(fin>>x>>y>>c)
    {
        mat[x].push_back({y,c});
        mat[y].push_back({x,c});
    }
    bfs(x);
    fout<<dist[y];
    return 0;
}