`M = 1xx2 + 2xx3 + 3xx4 + ...+2002xx2003`
`3M = 1xx2xx3 + 2xx3xx3 + 3xx4xx3 + ...+2002xx2003xx3`
`3M = 1xx2xx(3-0) + 2xx3xx(4-1) + 3xx4xx(5-2) + ...+2002xx2003xx(2004-2001)`
`3M = (1xx2xx3)-(1xx2xx0)+( 2xx3xx4)-(2xx3xx1) + (3xx4xx5)-(3xx4xx2) + ...+(2002xx2003xx2004)-(2002xx2004xx2001)`
`3M=2002xx2003xx2004`
`M=2002xx2003xx668`
ra số cụ thể thì to lắm nên mình k tính nhé
