Buggy python submission (verdict: Time Limit Exceeded):
#!/usr/bin/env python3
# Generated by https://github.com/kyuridenamida/atcoder-tools
import sys
import itertools
import collections

INF = 1145141919


def solve(S: int):
    l = list(reversed(str(S)))
    a = [int(l[c]) * 10**c for c in range(len(l))]

    def list_cumsum(l):
        return list(itertools.accumulate(l))
    s = [n % 2019 for n in list_cumsum([0]+a)]

    return sum([int(v * (v-1) / 2) for v in collections.Counter(s).values()])


def main():

    sys.setrecursionlimit(10 ** 6)

    def iterate_tokens():
        for line in sys.stdin:
            for word in line.split():
                yield word
    tokens = iterate_tokens()
    S = int(next(tokens))  # type: int
    print(solve(S))


if __name__ == '__main__':
    main()


Fixed submission:
#!/usr/bin/env python3
# Generated by https://github.com/kyuridenamida/atcoder-tools
import sys
import itertools
import collections

INF = 1145141919


def solve(S: int):
    l = list(reversed(str(S)))
    a = [int(l[c]) * pow(10, c, 2019) for c in range(len(l))]

    def list_cumsum(l):
        return list(itertools.accumulate(l))
    s = [n % 2019 for n in list_cumsum([0]+a)]

    return sum([int(v * (v-1) / 2) for v in collections.Counter(s).values()])


def main():

    sys.setrecursionlimit(10 ** 6)

    def iterate_tokens():
        for line in sys.stdin:
            for word in line.split():
                yield word
    tokens = iterate_tokens()
    S = int(next(tokens))  # type: int
    print(solve(S))


if __name__ == '__main__':
    main()

Buggy python submission (verdict: Time Limit Exceeded):
#!/usr/bin/env python3
# Generated by https://github.com/kyuridenamida/atcoder-tools
import sys
import itertools
import collections

INF = 1145141919


def solve(S: int):
    l = list(reversed(str(S)))
    a = [int(l[c]) * 10**c for c in range(len(l))]

    def list_cumsum(l):
        return list(itertools.accumulate(l))
    s = [n % 2019 for n in list_cumsum([0]+a)]

    return sum([sum(range(v)) for v in collections.Counter(s).values()])


def main():

    sys.setrecursionlimit(10 ** 6)

    def iterate_tokens():
        for line in sys.stdin:
            for word in line.split():
                yield word
    tokens = iterate_tokens()
    S = int(next(tokens))  # type: int
    print(solve(S))


if __name__ == '__main__':
    main()


Fixed submission:
#!/usr/bin/env python3
# Generated by https://github.com/kyuridenamida/atcoder-tools
import sys
import itertools
import collections

INF = 1145141919


def solve(S: int):
    l = list(reversed(str(S)))
    a = [int(l[c]) * pow(10, c, 2019) for c in range(len(l))]

    def list_cumsum(l):
        return list(itertools.accumulate(l))
    s = [n % 2019 for n in list_cumsum([0]+a)]

    return sum([int(v * (v-1) / 2) for v in collections.Counter(s).values()])


def main():

    sys.setrecursionlimit(10 ** 6)

    def iterate_tokens():
        for line in sys.stdin:
            for word in line.split():
                yield word
    tokens = iterate_tokens()
    S = int(next(tokens))  # type: int
    print(solve(S))


if __name__ == '__main__':
    main()

Buggy python submission (verdict: Time Limit Exceeded):
#!/usr/bin/env python3
# Generated by https://github.com/kyuridenamida/atcoder-tools
import sys

INF = 1145141919


def solve(S: int):
    ans = 0
    s = [0]+list(map(int, str(S)))
    for i in range(1, len(s)):
        s[i] = s[i-1]*10+s[i]
    for i in range(len(s)-4):
        for j in range(i + 4, len(s)):
            if (s[j] - s[i]*10**(j-i)) % 2019 == 0:
                ans += 1

    return ans


def main():

    sys.setrecursionlimit(10 ** 6)

    def iterate_tokens():
        for line in sys.stdin:
            for word in line.split():
                yield word
    tokens = iterate_tokens()
    S = int(next(tokens))  # type: int
    print(solve(S))


if __name__ == '__main__':
    main()


Fixed submission:
#!/usr/bin/env python3
# Generated by https://github.com/kyuridenamida/atcoder-tools
import sys
import itertools
import collections

INF = 1145141919


def solve(S: int):
    l = list(reversed(str(S)))
    a = [int(l[c]) * pow(10, c, 2019) for c in range(len(l))]

    def list_cumsum(l):
        return list(itertools.accumulate(l))
    s = [n % 2019 for n in list_cumsum([0]+a)]

    return sum([int(v * (v-1) / 2) for v in collections.Counter(s).values()])


def main():

    sys.setrecursionlimit(10 ** 6)

    def iterate_tokens():
        for line in sys.stdin:
            for word in line.split():
                yield word
    tokens = iterate_tokens()
    S = int(next(tokens))  # type: int
    print(solve(S))


if __name__ == '__main__':
    main()