uses crt;
const eps: real = 0.000000001;
var  dau: integer;
     i: longint;
     s: real;
BEGIN
    CLRSCR;

    s:= 0;
    dau:= 1;
    i:= 1;
    while 4/i>=eps do
    begin
        s:= s + dau*4/i;
        i:=i+2;
        dau:= -dau;
    end;
    writeln('Ket qua: ', s:0:9);

    READLN;
END.