program factorial;
var i,min,p:integer;
    n,m,t:longint;
    f,g:text;
    bool:boolean;
begin
assign (f,'fact.in');
reset(f);
assign (g,'fact.out');
rewrite(g);
read (f, p);
i:=0;
bool:=false;
n:=1;
repeat
        i:=i+1;
        n:=n*i;
        t:=n;
        m:=p;
        min:=0;
        repeat
                bool:=true;
                if (m<>0) and (t mod 10 = 0) then begin
                m:=m-1;
                t:=t div 10; end
                else bool:=false;
        until ((m=0) or (bool=false));
until bool = true;

write(g, i);

close(f);
close(g);
end.