DIENTICH PASCAL

var r, s,c,st:real;
begin
    assign(input, 'dientich.inp');reset(input);
    assign(output, 'dientich.out');rewrite(output);
    read(s);
    c:=sqrt(s);
    r:=c/2;
    st:=r*r*3.14;
    writeln('dien tich hinh tron la ',st:0:6);
end.