Buggy python submission (verdict: Time Limit Exceeded):
#!/usr/bin/env python3
import sys
import collections


def solve(S: int):
    S = list(map(int, list(str(S))))
    count = collections.defaultdict(int)

    count[0] = 1
    tmp = ''
    prev_modulo = 0
    for idx, s in enumerate(S[::-1]):
        prev_modulo = (s * (10 ** idx) + prev_modulo) % 2019
        count[prev_modulo] += 1

    result = 0
    for k, v in count.items():
        result += v * (v-1) // 2
    print(result)
    return


# Generated by 1.1.6 https://github.com/kyuridenamida/atcoder-tools  (tips: You use the default template now. You can remove this line by using your custom template)
def main():
    def iterate_tokens():
        for line in sys.stdin:
            for word in line.split():
                yield word
    tokens = iterate_tokens()
    S = int(next(tokens))  # type: int
    solve(S)

if __name__ == '__main__':
    main()


Fixed submission:
#!/usr/bin/env python3
import sys
import collections

def solve(S: int):
    S = list(map(int, list(str(S))))
    count = collections.defaultdict(int)

    count[0] = 1
    tmp = ''
    prev_modulo = 0
    for idx, s in enumerate(S[::-1]):
        prev_modulo = (s * pow(10, idx, 2019) + prev_modulo) % 2019
        count[prev_modulo] += 1

    result = 0
    for k, v in count.items():
        result += v * (v-1) // 2
    print(result)
    return


# Generated by 1.1.6 https://github.com/kyuridenamida/atcoder-tools  (tips: You use the default template now. You can remove this line by using your custom template)
def main():
    def iterate_tokens():
        for line in sys.stdin:
            for word in line.split():
                yield word
    tokens = iterate_tokens()
    S = int(next(tokens))  # type: int
    solve(S)

if __name__ == '__main__':
    main()

Buggy python submission (verdict: Time Limit Exceeded):
#!/usr/bin/env python3
import sys
import collections


def solve(S: int):
    S = str(S)

    count = collections.defaultdict(int)
    count[0] = 1
    tmp = ''
    prev_modulo = 0
    for idx, s in enumerate(S[::-1]):
        s = int(s)
        prev_modulo = (s * (10 ** idx) + prev_modulo) % 2019
        count[prev_modulo] += 1

    result = 0
    for k, v in count.items():
        result += v * (v-1) // 2
    print(result)
    return


# Generated by 1.1.6 https://github.com/kyuridenamida/atcoder-tools  (tips: You use the default template now. You can remove this line by using your custom template)
def main():
    def iterate_tokens():
        for line in sys.stdin:
            for word in line.split():
                yield word
    tokens = iterate_tokens()
    S = int(next(tokens))  # type: int
    solve(S)

if __name__ == '__main__':
    main()


Fixed submission:
#!/usr/bin/env python3
import sys
import collections

def solve(S: int):
    S = list(map(int, list(str(S))))
    count = collections.defaultdict(int)

    count[0] = 1
    tmp = ''
    prev_modulo = 0
    for idx, s in enumerate(S[::-1]):
        prev_modulo = (s * pow(10, idx, 2019) + prev_modulo) % 2019
        count[prev_modulo] += 1

    result = 0
    for k, v in count.items():
        result += v * (v-1) // 2
    print(result)
    return


# Generated by 1.1.6 https://github.com/kyuridenamida/atcoder-tools  (tips: You use the default template now. You can remove this line by using your custom template)
def main():
    def iterate_tokens():
        for line in sys.stdin:
            for word in line.split():
                yield word
    tokens = iterate_tokens()
    S = int(next(tokens))  # type: int
    solve(S)

if __name__ == '__main__':
    main()

Buggy python submission (verdict: Time Limit Exceeded):
#!/usr/bin/env python3
import sys
import collections


def solve(S: int):
    S = str(S)

    count = collections.defaultdict(int)
    count[0] = 1
    tmp = ''
    for idx, s in enumerate(S[::-1]):
        digit = int(S[-idx:])
        count[digit % 2019] += 1
    
    result = 0
    for k, v in count.items():
        result += v * (v-1) // 2
    print(result)
    return


# Generated by 1.1.6 https://github.com/kyuridenamida/atcoder-tools  (tips: You use the default template now. You can remove this line by using your custom template)
def main():
    def iterate_tokens():
        for line in sys.stdin:
            for word in line.split():
                yield word
    tokens = iterate_tokens()
    S = int(next(tokens))  # type: int
    solve(S)

if __name__ == '__main__':
    main()


Fixed submission:
#!/usr/bin/env python3
import sys
import collections

def solve(S: int):
    S = list(map(int, list(str(S))))
    count = collections.defaultdict(int)

    count[0] = 1
    tmp = ''
    prev_modulo = 0
    for idx, s in enumerate(S[::-1]):
        prev_modulo = (s * pow(10, idx, 2019) + prev_modulo) % 2019
        count[prev_modulo] += 1

    result = 0
    for k, v in count.items():
        result += v * (v-1) // 2
    print(result)
    return


# Generated by 1.1.6 https://github.com/kyuridenamida/atcoder-tools  (tips: You use the default template now. You can remove this line by using your custom template)
def main():
    def iterate_tokens():
        for line in sys.stdin:
            for word in line.split():
                yield word
    tokens = iterate_tokens()
    S = int(next(tokens))  # type: int
    solve(S)

if __name__ == '__main__':
    main()

Buggy python submission (verdict: Time Limit Exceeded):
#!/usr/bin/env python3
import sys
import collections


def solve(S: int):
    S = str(S)

    count = collections.defaultdict(int)
    count[0] = 1
    tmp = ''
    for s in S[::-1]:
        tmp = s + tmp
        digit = int(tmp)
        count[digit % 2019] += 1
    result = 0
    for k, v in count.items():
        result += v * (v-1) // 2
    print(result)
    return


# Generated by 1.1.6 https://github.com/kyuridenamida/atcoder-tools  (tips: You use the default template now. You can remove this line by using your custom template)
def main():
    def iterate_tokens():
        for line in sys.stdin:
            for word in line.split():
                yield word
    tokens = iterate_tokens()
    S = int(next(tokens))  # type: int
    solve(S)

if __name__ == '__main__':
    main()


Fixed submission:
#!/usr/bin/env python3
import sys
import collections

def solve(S: int):
    S = list(map(int, list(str(S))))
    count = collections.defaultdict(int)

    count[0] = 1
    tmp = ''
    prev_modulo = 0
    for idx, s in enumerate(S[::-1]):
        prev_modulo = (s * pow(10, idx, 2019) + prev_modulo) % 2019
        count[prev_modulo] += 1

    result = 0
    for k, v in count.items():
        result += v * (v-1) // 2
    print(result)
    return


# Generated by 1.1.6 https://github.com/kyuridenamida/atcoder-tools  (tips: You use the default template now. You can remove this line by using your custom template)
def main():
    def iterate_tokens():
        for line in sys.stdin:
            for word in line.split():
                yield word
    tokens = iterate_tokens()
    S = int(next(tokens))  # type: int
    solve(S)

if __name__ == '__main__':
    main()