var f,g:text;
    n,p,nr,i,p1:int64;
    ok:boolean;
begin
     assign(f,'fact.in');
     assign(g,'fact.out');
     reset(f);
     rewrite(g);
{-rezolvarea problemei------------------------------}
     read(f,n);
     p:=1;
     nr:=0;
     ok:=true;
     i:=1;
     repeat
           p:=p*i;
           if p mod 5=0 then
           begin
                p1:=p;
                while ok=true do
                begin
                     if p1 mod 5=0 then
                     begin
                          inc(nr);
                          ok:=true;
                     end
                     else ok:=false;
                     p1:=p1 div 5;
                end;
           end;
           i:=i+1;
     until nr=n;
     write(g,nr);
{---------------------------------------------------}
     close(g);
     close(f);end.