program Project1;
{$APPTYPE CONSOLE}
Label 1;
var R,R1,R2:REAL;
begin
1:Writeln('Vvedit opir R1 i R2');
readln(R1,R2);
IF (R1<=0) OR (R2<=0) THEN begin
WRITELN('Opir ne isnue');
goto 1;end else
R:=(R1*R2)/(R1+R2);
writeln('Sumarnyi opir R=',R:4:2);
readln;
end.