var a:array[1..50,1..50] of integer;
    k,x,y,c,m,n:integer;
    f:text;
function arc(i,j:integer):boolean;
var k:integer;
    ok:boolean;
begin
ok:=false;
for k:=1 to m do
   if (a[x,k]=1) and (a[y,k]=-1) then ok:=true;
arc:=ok;
end;
begin
assign(f,'graf.txt ');reset(f);
readln(f,n,m,x,y);
c:=0;
for k:=1 to m do begin
                 inc(c);
                 readln(f,x,y);
                 a[x,c]:=1;
                 a[y,c]:=-1;
                 end;
close(f);
if arc(x,y) then write('exista arc intre ',x,' si ',y);
readln;
end.