PROGRAM Ce;
CONST
p1 = 3.14159;
VAR
dlina : Real;
Square, Len : Real;
BEGIN
WriteLn('dlina');

Read (dlina);

Len :=dlina /(2 * p1);

Square := p1 * sqr(Len);

WriteLn('s= ', Square :6:2);
readln;
END.