Buggy python submission (verdict: Runtime Error):
# import bisect
# import heapq
# import math
# import random
# import sys
# from collections import Counter, defaultdict
# from decimal import ROUND_CEILING, ROUND_HALF_UP, Decimal
# from functools import lru_cache, reduce
# from itertools import combinations, combinations_with_replacement, product


def read_int():
    return int(input())


def read_int_n():
    return list(map(int, input().split()))


def read_float():
    return float(input())


def read_float_n():
    return list(map(float, input().split()))


def read_str():
    return input()


def read_str_n():
    return list(map(str, input().split()))


def error_print(*args, **kwargs):
    print(*args, **kwargs, file=sys.stderr)


def mt(f):
    import time

    def wrap(*args, **kwargs):
        s = time.time()
        ret = f(*args, **kwargs)
        e = time.time()

        error_print(e - s, 'sec')
        return ret

    return wrap


# @mt
def slv(A, B, C, K):
    ans = A - B if K % 2 == 0 else B - A
    if abs(ans) > 1e+18:
        return 'Unfair'
    return ans


def main():
    A, B, C, K = read_int_n()

    print(slv(A, B, C, K))


if __name__ == '__main__':
    main()


Fixed submission:
import bisect
import heapq
import math
import random
import sys
from collections import Counter, defaultdict
from decimal import ROUND_CEILING, ROUND_HALF_UP, Decimal
from functools import lru_cache, reduce
from itertools import combinations, combinations_with_replacement, product


def read_int():
    return int(input())


def read_int_n():
    return list(map(int, input().split()))


def read_float():
    return float(input())


def read_float_n():
    return list(map(float, input().split()))


def read_str():
    return input()


def read_str_n():
    return list(map(str, input().split()))


# @mt
def slv(A, B, C, K):
    ans = A - B if K % 2 == 0 else B - A
    if abs(ans) > 1e+18:
        return 'Unfair'
    return ans


def main():
    A, B, C, K = read_int_n()

    print(slv(A, B, C, K))


if __name__ == '__main__':
    main()

Buggy python submission (verdict: Runtime Error):
import bisect
import heapq
import math
import random
import sys
from collections import Counter, defaultdict
from decimal import ROUND_CEILING, ROUND_HALF_UP, Decimal
from functools import lru_cache, reduce
from itertools import combinations, combinations_with_replacement, product


def read_int():
    return int(input())


def read_int_n():
    return list(map(int, input().split()))


def read_float():
    return float(input())


def read_float_n():
    return list(map(float, input().split()))


def read_str():
    return input()


def read_str_n():
    return list(map(str, input().split()))


def error_print(*args, **kwargs):
    print(*args, **kwargs, file=sys.stderr)


def mt(f):
    import time

    def wrap(*args, **kwargs):
        s = time.time()
        ret = f(*args, **kwargs)
        e = time.time()

        error_print(e - s, 'sec')
        return ret

    return wrap


# @mt
def slv(A, B, C, K):
    ans = A - B if K % 2 == 0 else B - A
    if abs(ans) > 1e+18:
        return 'Unfair'
    return ans


def main():
    A, B, C, K = read_int_n()

    print(slv(A, B, C, K))


if __name__ == '__main__':
    main()


Fixed submission:
import bisect
import heapq
import math
import random
import sys
from collections import Counter, defaultdict
from decimal import ROUND_CEILING, ROUND_HALF_UP, Decimal
from functools import lru_cache, reduce
from itertools import combinations, combinations_with_replacement, product


def read_int():
    return int(input())


def read_int_n():
    return list(map(int, input().split()))


def read_float():
    return float(input())


def read_float_n():
    return list(map(float, input().split()))


def read_str():
    return input()


def read_str_n():
    return list(map(str, input().split()))


# @mt
def slv(A, B, C, K):
    ans = A - B if K % 2 == 0 else B - A
    if abs(ans) > 1e+18:
        return 'Unfair'
    return ans


def main():
    A, B, C, K = read_int_n()

    print(slv(A, B, C, K))


if __name__ == '__main__':
    main()

Buggy python submission (verdict: Runtime Error):
import bisect
import heapq
import math
import random
import sys
from collections import Counter, defaultdict
from decimal import ROUND_CEILING, ROUND_HALF_UP, Decimal
from functools import lru_cache, reduce
from itertools import combinations, combinations_with_replacement, product


def read_int():
    return int(input())


def read_int_n():
    return list(map(int, input().split()))


def read_float():
    return float(input())


def read_float_n():
    return list(map(float, input().split()))


def read_str():
    return input()


def read_str_n():
    return list(map(str, input().split()))


def error_print(*args, **kwargs):
    print(*args, **kwargs, file=sys.stderr)


def mt(f):
    import time

    def wrap(*args, **kwargs):
        s = time.time()
        ret = f(*args, **kwargs)
        e = time.time()

        error_print(e - s, 'sec')
        return ret

    return wrap


@mt
def slv(A, B, C, K):
    ans = A - B if K % 2 == 0 else B - A
    if ans > 1e+18:
        return 'Unfair'
    return ans


def main():
    A, B, C, K = read_int_n()

    print(slv(A, B, C, K))


if __name__ == '__main__':
    main()


Fixed submission:
import bisect
import heapq
import math
import random
import sys
from collections import Counter, defaultdict
from decimal import ROUND_CEILING, ROUND_HALF_UP, Decimal
from functools import lru_cache, reduce
from itertools import combinations, combinations_with_replacement, product


def read_int():
    return int(input())


def read_int_n():
    return list(map(int, input().split()))


def read_float():
    return float(input())


def read_float_n():
    return list(map(float, input().split()))


def read_str():
    return input()


def read_str_n():
    return list(map(str, input().split()))


# @mt
def slv(A, B, C, K):
    ans = A - B if K % 2 == 0 else B - A
    if abs(ans) > 1e+18:
        return 'Unfair'
    return ans


def main():
    A, B, C, K = read_int_n()

    print(slv(A, B, C, K))


if __name__ == '__main__':
    main()