var id,id1,cs,ct,viz,x,s:array[0..200010] of longint;
    a,b,i,j,n,m,p,u,q,t:longint;

begin
assign(input,'sate.in');reset(input);
assign(output,'sate.out');rewrite(output);
readln(n,m,a,b);
for i:=1 to m do
        begin
        readln(p,q,t);
        inc(id[p]);
        inc(id[q]);
        end;
for i:=1 to n do
        id[i]:=id[i]+id[i-1];
reset(input);
readln(n,m,a,b);
for i:=1 to m do
        begin
        readln(p,q,t);
        inc(ct[p]);
        inc(ct[q]);
        x[id[p-1]+ct[p]]:=q;
        x[id[q-1]+ct[q]]:=p;
        cs[id[p-1]+ct[p]]:=t;
        cs[id[q-1]+ct[q]]:=t;
        end;
fillchar(ct,sizeof(ct),0);
s[1]:=a;
p:=1;u:=1;
while p<=u do
        begin
        for i:=id[s[p]-1]+1 to id[s[p]] do
                begin
                if viz[x[i]]=0 then
                        begin
                        inc(u);
                        s[u]:=x[i];
                        viz[x[i]]:=1;
                        if x[i]<s[p] then
                                ct[x[i]]:=ct[s[p]]-cs[i]
                        else
                                ct[x[i]]:=ct[s[p]]+cs[i];
                        if x[i]=b then
                                begin
                                writeln(ct[x[i]]);
                                close(output);
                                halt;
                                end;
                        end;
                end;
        inc(p);
        end;
close(input);close(output);
end.