#include <cstdio>
#include <queue>
using namespace std;
const int maxn=30001;
queue <int> q;
bool viz[maxn];
int d[maxn],cap[maxn],nxt[2*maxn],nr;
struct muchie
{
int nod,cost;
}val[2*maxn];
inline void add(int a,int b,int c)
{
val[++nr].nod=b;val[nr].cost=c;
nxt[nr]=cap[a];
cap[a]=nr;
}
inline void bfs(int x,int y)
{
int a,b,c,p;
q.push(x);viz[x]=true;
while(!viz[y])
{
a=q.front();q.pop();
p=cap[a];
while(p)
{
b=val[p].nod;c=val[p].cost;
if(!viz[b])
{
viz[b]=true;
d[b]=d[a]+c;
q.push(b);
}
p=nxt[p];
}
}
}
int main()
{
FILE *fin,*fout;
fin=fopen("sate.in","r");
fout=fopen("sate.out","w");
int n,m,x,y,a,b,c;
fscanf(fin,"%d%d%d%d",&n,&m,&x,&y);
for(int i=0;i<m;i++)
{
fscanf(fin,"%d%d%d",&a,&b,&c);
add(a,b,c);add(b,a,-c);
}
bfs(x,y);
fprintf(fout,"%d",d[y]);
fclose(fin);
fclose(fout);
return 0;
}