program factorial;

var f : text;
    x,s,p,n : longint;

begin
    assign(f,'fact.in'); reset(f);
    read(f,x);
    close(f);

    s := 0; p := 0; n := 1;

    while p < x do begin
        s := s+1;
        n := n * s;
        while n mod 10 = 0 do begin
            n := n div 10;
            p := p+1;
            end;
        n := n mod 10;
        end;

    assign(f,'fact.out'); rewrite(f);
    write(f,s);
    close(f);

end.