var p,n,i: integer;
    f,g:text;
begin
     assign(f,'fact.in');
     assign(g,'fact.out');
     reset(f); read(f,p); close(f);
     i:=0;
     while p<>0 do
     begin
        inc(i);
        while i mod 5=0 do
                begin
                        i:=i div 5;
                        dec(p);
                end;
     end;
     rewrite(g); write(g,i); close(g);
end.