programm kainushi;
var i, F, p, S, V: real;
begin
readln ( i, F, p, S)
V: = (1/2 * i) * (F/p*S) / 2
writeln ('V=', V)
end.
programm kainushi;
var i, F, p, S, V: real;
begin
readln ( i, F, p, S)
V: = (1/2 * i) * (F/p*S) / 2
writeln ('V=', V)
end.