program Zadacha1;
{$APPTYPE CONSOLE}
var S,N,D,m:integer;
begin
writeln('Vvedit masu Darynky');
readln(D);
N:=D-5;
writeln('Vvedit masu cukerok');
readln(m);
S:=m-(D+N);
writeln(S/2:1:2);
readln;
end.