=1+(1+2+3+4+5+6+7+8+9+10+11+12+13+14+15+16+17+18+19+280+21+22+23+24+25+26+27+28+29+30)
=1+(1+30)×30÷2
=1+31×30÷2
=1+930÷2
=1+465
=466
=1+(1+2+3+4+5+6+7+8+9+10+11+12+13+14+15+16+17+18+19+280+21+22+23+24+25+26+27+28+29+30)
=1+(1+30)×30÷2
=1+31×30÷2
=1+930÷2
=1+465
=466