var f,g:text;
    x,k,l,p,j,s,n,i,b:longint;
   function styo(x:longint):longint;
   begin
   k:=x;
   j:=0;
   while k mod 5=0 do
   begin
   k:=k div 5;
   j:=j+1;
   end;
   styo:=j
   end;
begin
assign(f,'fact.in');
assign(g,'fact.out');
reset(f);
rewrite(g);
 read(f,n);
 b:=1;
 s:=0;
while s<n do
begin
b:=b+1;
s:=s+styo(b);
end;
write(g,b);
close(f);
close(g);
end.