#include<bits/stdc++.h>
using namespace std;
const int maxn=1e6+10,lg=21;
struct yal{
int u,v,w;
int getad(int fu){
int ret=(u^v^fu);
return ret;
}
};
yal alled[maxn];
vector<int>adj[maxn];
int n,m,visa[maxn],lca[lg][maxn*2],wtf[2*maxn],ghabl[maxn],vis[maxn],high[maxn],timea,para[maxn],s,t;
pair<int,int>stf[maxn];
int dp[(1<<20)][20];
vector<int>allind[(1<<20)];
vector<int>allv;
vector<int>z;
void aval(){
for(int i=1;i<(1<<20);i++)
{
int j=0;
for(;;j++){
if((i>>j)&1){
break;
}
}
allind[i]=allind[i^(1<<j)];
allind[i].push_back(j);
}
int ha=-1;
for(int i=1;i<2*maxn;i++){
if(__builtin_popcount(i)==1){
ha++;
}
wtf[i]=ha;
}
}
void dfs(int u,int par=0){
high[u]=high[par]+1;
z.push_back(u);
stf[u].first=(int)z.size()-1;
for(auto x:adj[u]){
int v=alled[x].getad(u);
if(v!=par){
if(v!=alled[x].v){
swap(alled[x].u,alled[x].v);
}
para[v]=x;
dfs(v,u);
z.push_back(u);
}
}
stf[u].second=(int)z.size()-1;
}
inline void callca(){
for(int i=0;i<lg;i++){
for(int j=0;j<(int)z.size();j++){
if(i==0){
lca[i][j]=z[j];
continue;
}
if(high[lca[i-1][j]]<high[lca[i-1][j+(1<<(i-1))]]){
lca[i][j]=lca[i-1][j];
}
else{
lca[i][j]=lca[i-1][j+(1<<(i-1))];
}
}
}
}
inline int getlca(int u,int v){
int fu=min(stf[u].first,stf[v].first);
int fv=max(stf[u].first,stf[v].first);
u=fu;
v=fv;
int len=v-u+1;
int te=wtf[len];
if(high[lca[te][u]]<high[lca[te][v-(1<<te)+1]]){
return lca[te][u];
}
return lca[te][v-(1<<te)+1];
}
inline int dis(int u,int v){
int uv=getlca(u,v);
int ret=high[u]+high[v]-2*high[uv];
return ret;
}
void solve(int u){
//cout<<u<<endl;
if(vis[u]==1){
return ;
}
if(visa[u]==1){
cout<<-1<<"\n";
exit(0);
}
visa[u]=1;
solve(alled[para[u]].getad(u));
if(alled[para[u]].w!=0){
allv.push_back(para[u]);
solve(alled[para[u]].w);
}
vis[u]=1;
return ;
}
void calghabl(int u,int par=0){
ghabl[u]+=ghabl[par];
for(auto x:adj[u]){
int v=alled[x].getad(u);
if(v!=par){
calghabl(v,u);
}
}
}
int main()
{
ios::sync_with_stdio(0);
cin.tie(0);
cout.tie(0);
aval();
cin>>n;
cin>>s>>t;
for(int i=0;i<n-1;i++){
cin>>alled[i].u>>alled[i].v>>alled[i].w;
adj[alled[i].u].push_back(i);
adj[alled[i].v].push_back(i);
}
dfs(s);
callca();
vis[s]=1;
solve(t);
m=allv.size();
for(int i=0;i<m;i++){
ghabl[alled[allv[i]].v]+=(1<<i);
}
calghabl(s);
for(int i=1;i<(int)(1<<m);i++){
for(auto x:allind[i]){
int fake=1e9;
if((ghabl[alled[allv[x]].u]&i)!=ghabl[alled[allv[x]].u]||(ghabl[alled[allv[x]].w]&i)!=ghabl[alled[allv[x]].w]){
dp[i][x]=fake;
continue;
}
if(__builtin_popcount(i)==1){
dp[i][x]=dis(alled[allv[x]].u,alled[allv[x]].w)+dis(alled[allv[x]].w,s);
continue;
}
for(auto y:allind[i^(1<<x)]){
fake=min(fake,dis(alled[allv[y]].u,alled[allv[x]].w)+dis(alled[allv[x]].u,alled[allv[x]].w)+dp[(1<<x)^i][y]);
}
dp[i][x]=fake;
}
}
if(m==0){
int res=dis(s,t);
cout<<res<<"\n";
return 0;
}
else{
int res=1e9;
for(auto x:allind[(1<<m)-1]){
res=min(res,dp[(1<<m)-1][x]+dis(alled[allv[x]].u,t));
}
cout<<res<<"\n";
}
}
