VAR s:REAL;
n,i:INTEGER;
FUNCTION Giaithua(n:INTEGER):LONGINT;
VAR s,i:LONGINT;
BEGIN               
    s:=1;
FOR i:=n DOWNTO 1 DO
s:=s*i;
Giaithua:=s;
END;
BEGIN
    Write('Nhap n : ');
    Readln(n);      
    s:=0;
    FOR i:=0 TO n DO
    s:=s+1/giaithua(i);
    Write('S= ',s:4:4);
    Readln;
END.