1) n = int(input()) sum = (n * (n + 1)) // 2
2) number = input() digit = int(input()) count = number.count(str(digit))
3) A, B = map(int, input().split()) C = A while (C * (C + 1)) // 2 <= 2 * B: C += 1 print(C - 1)
4) n = int(input()) factorial = 1 for i in range(1, n + 1): factorial *= i print(factorial)
5) n = int(input()) sum = 0 for i in range(1, n + 1): sum += i * (3 + i % 3) print(sum)
6) number = input() digit = int(input()) index = number.rfind(str(digit)) + 1 print(index)