19+199+1999+19999+199999+1999999+.+1999个1999=（19+1+199+1+1999+1+19999+1+199999+1+1999999+1-6）+1999个1999=(20+200+2000+20000+200000+2000000-6)+1999+1个1999+1-2=（2222220-6）+2000个2000-2=2222214+400...