87654321⋅99999 + 87654320 вычислить с упрощением
87654321 * 99999 + 87654321 - 1 = 87654321 * 100000 - 1 = 8765432099999
87654321*99999 +87654320 = 87654321*99999 +87654321 -1 = 87654321(99999 +1) -1 = 87654321*100000 -1 = 8765432100000 -1 = 8765432099999