Bellman-Ford

type
    edge = record
        a,b,cost:longint;
end;

const
   count = 1000;
   inf = 1000000;

var
    e:array[1..count] of edge;
    d:array[1..count] of longint;
    i,j,n,m,v1,v2:longint;

Begin
  read(n,m,v1,v2);
  for i:=1 to m do
    read(e[i].a,e[i].b,e[i].cost);
  for i:=1 to n do
    d[i]:=inf;
  d[v1]:=0;
  for i:=1 to n do
     for j:=1 to m do
       if (d[e[j].b] > d[e[j].a] + e[j].cost) and (d[e[j].a] < inf) then
           d[e[j].b] := d[e[j].a] + e[j].cost;
  write(d[v2]);
end.