var f,f2:text;
    n,fac,p,co,nfac:longint;
begin
assign(f,'fact.in');
assign(f2,'fact.out');
reset(f);
readln(f,n);
close(f);
if n=0 then fac:=0
else
 begin
  fac:=0;
  co:=0;
  while (co+31<n) do
   begin
    fac:=fac+125;
    co:=co+31;
   end;
  while (co<n) do
   begin
    nfac:=fac+5;
    fac:=fac+5;
    p:=0;
    while nfac mod 5=0 do
     begin
      nfac:=nfac div 5;
      p:=p+1;
     end;
    co:=co+p;
   end;
 end;
rewrite(f2);
writeln(f2,fac);
close(f2);
end.