var f,g:text;
    n,p,nr,i:int64;
    ok:boolean;
begin
     assign(f,'fact.in');
     assign(g,'fact.out');
     reset(f);
     rewrite(g);
{-rezolvarea problemei------------------------------}
     read(f,n);
     p:=1;
     for i:=1 to n do
         p:=p*i;
     nr:=0;
     ok:=true;
     while ok=true do
     begin
          if p mod 5=0 then
          begin
               inc(nr);
               ok:=true;
          end
          else ok:=false;
          p:=p div 5;
     end;
     write(g,nr);
{---------------------------------------------------}
     close(g);
     close(f);end.