87654321⋅99999 + 87654320 вычислить с упрощением

87654321*99999 +87654320 =
87654321*99999 +87654321 -1 =
87654321(99999 +1) -1 =
87654321*100000 -1 =
8765432100000 -1 =
8765432099999

87654321 * 99999 + 87654321 - 1 = 87654321 * 100000 - 1 = 8765432099999