var p,i,n5,n,c:longint;
    f1,f2:text;
begin
assign(f1,'fact.in');
assign(f2,'fact.out');
reset(f1);
rewrite(f2);
readln(f1,p);
n:=0;n5:=0;
repeat
 n:=n+1;
 c:=n;
 while c mod 5=0 do
  begin
   c:=c div 5;
   n5:=n5+1;
  end;
until n5=p;
writeln(f2,n);
close(f1);
close(f2);
end.