program factorial;
var f,g:text;
    min,i,e,p,x,y:longint;
begin
assign(f,'fact.in');
reset(f);
assign(g,'fact.out');
rewrite(g);
read(f,p);
i:=0;
min:=0;
while(min<p) do
 begin
 e:=e+1; i:=e;
 while(i mod 2=0) do
  begin
   x:=x+1;
   i:=i div 2;
  end;
 while(i mod 5=0) do
  begin
   y:=y+1;
   i:=i div 5;
  end;
 if x<y then min:=x else min:=y;
 if x=y then min:=x;
 if min>=p then break;
end;
write(g,e);
close(f);
close(g);
end.