var  p:longint;

procedure citire;
var f:text;
begin
     assign(f,'factorial.in');
     reset(f);
     read(f,p);
     close(f);
end;

function determinare:longint;
var k,n,i,m:longint;
begin
     n:=0;i:=0;k:=0;
     while k<p do
     begin
          inc(n);m:=n;
          while m mod 5=0 do
          begin
               inc(k);
               m:=m div 5;
          end;
          if k>p then
                n:=-1;
     end;
     determinare:=n;
end;

procedure afisare;
var g:text;
begin
     assign(g,'factorial.out');
     rewrite(g);
     write(g,determinare);
     close(g);
end;

begin
     citire;
     determinare;
     afisare;
end.