uses crt;
var i,giaithua:integer;
    s:real;
begin
    clrscr;
    write('Nhap N: '); readln(n);
    s:=0; giaithua:=1;
    for i:=1 to n do
        begin
            giaithua:=giaithua*i;
            s:=s+1/giaithua;
        end;
    write('Tong S= ',s);
    readln;
end.