Program Factorial;
var f,g:text;
    p,n,nrp,x,y:integer;
Begin
 assign(f,'fact.in');
 reset(f);
 read(f,p);
 close(f);
If p>0 then
 Begin
 x:=5;
 nrp:=0;
 End;
While nrp<p do
 Begin
 x:=x+5;
 y:=x;
 End;
While (y mod 5=0) do
  Begin
  nrp:=nrp+1;
  y:=y div 5;
  End;
If nrp=p then
 n:=nrp;
assign(g,'fact.out');
rewrite(g);
writeln(g,n);
End.