#include <bits/stdc++.h>
using namespace std;
const int inf = 1e5 + 9;
vector<pair<int, int>> tree[inf];
map<pair<int, int>, int> m;
int dist[inf];
int par[inf];
bool vis[inf];
void dfss(int here, int len) {
dist[here] = len;
for (auto i : tree[here]) {
int there = i.first;
int nlen = len + i.second;
if (dist[there] == -1) dfss(there, nlen);
}
}
void dfsm(int here) {
vis[here] = true;
for (auto i : tree[here]) {
if (vis[i.first]) continue;
dfsm(i.first);
par[i.first] = here;
}
}
int main() {
ios::sync_with_stdio(0);
cin.tie(0); cout.tie(0);
int n, x, y; cin >> n >> x >> y;
for (int i = 0; i < n - 1; i++) {
int a, b, c; cin >> a >> b >> c;
tree[a].emplace_back(b, c);
tree[b].emplace_back(a, c);
m[make_pair(a, b)] = c;
m[make_pair(b, a)] = c;
}
fill(&dist[1], &dist[n + 1], -1);
dfss(x, 0);
dfsm(x);
int here = y;
int mpath = 0;
while (here != x) {
mpath = max(mpath, m[make_pair(here, par[here])]);
here = par[here];
}
cout << dist[y] - mpath << '\n';
}
