var p,x,i:longint;
		f:text;

function otos(a:longint):longint;
var i:longint;
begin
 i:=0;
 while (a mod 5)=0 do
 begin
 	inc(i);
 	a:=a div 5;
 end;
 otos:=i;
end;

begin
 assign(f,'fact.in');
 reset(f);
 read(f,p);
 close(f);
 i:=1;

 repeat
  x:=x+otos(i);
  inc(i);
 until p=x;
 dec(i);
 assign(f,'fact.out');
 rewrite(f);
 write(f,i);
 close(f);
end.