Buggy python submission (verdict: Runtime Error):
import sys
import math
from collections import deque


def main():
    n_d_a = sys.stdin.readline().strip().split(' ')
    n, d, a = [int(s) for s in n_d_a]

    xh = [None] * n

    for i in range(n):
        x, h = [int(s) for s in sys.stdin.readline().strip().split(' ')]
        xh[i] = [x, h]
    xh.sort()

    cur = 0
    attack_rightmost_idx = [-1] * n
    for i in range(n):
        if cur == n:
            attack_rightmost_idx[i] = n-1
            continue
        attack_rightmost_idx[i] = cur
        x, h = xh[i]
        attack_rightmost = x + 2 * d
        while cur < n and xh[cur][0] <= attack_rightmost:
            attack_rightmost_idx[i] = cur
            cur += 1

    events = deque()
    total_damage = 0
    ans = 0
    for i in range(n):
        while events and events[0][0] <= i:
            total_damage += events[0][1]
            events.popleft()

        x, h = xh[i]

        remaining_life = h - total_damage
        if remaining_life <= 0:
            continue

        needed = math.ceil(remaining_life / a)
        ans += needed
        total_damage += needed * a
        events.append((attack_rightmost_idx[i]+1, - needed * a))

    print(ans)


if __name__ == '__main__':
    main()


Fixed submission:
import sys

def main():
    h_and_n_s = sys.stdin.readline().strip().split(' ')
    h, n = [int(s) for s in h_and_n_s]
    a = [-1] * n
    b = [-1] * n

    # max_a = 0
    # ef_i = -1
    for i in range(n):
        a[i], b[i] = [int(s) for s in sys.stdin.readline().strip().split(' ')]
        # max_a = max(max_a, a[i])
        # if a[ef_i] / b[ef_i] < a[i] / b[i]:
        #     ef_i = i

    dp = [float('inf')] * (h+1)

    for point in range(h+1):
        for i in range(n):
            if point <= a[i]:
                dp[point] = min(dp[point], b[i])
                continue

            dp[point] = min(dp[point], dp[point-a[i]] + b[i])

    print(dp[h])


if __name__ == '__main__':
    main()

Buggy python submission (verdict: Time Limit Exceeded):
import sys
import math

def main():
    h_and_n_s = sys.stdin.readline().strip().split(' ')
    h, n = [int(s) for s in h_and_n_s]
    a = [-1] * n
    b = [-1] * n

    for i in range(n):
        a[i], b[i] = [int(s) for s in sys.stdin.readline().strip().split(' ')]

    dp = [float('inf')] * (h+1)

    for point in range(h+1):
        for i in range(n):
            if point <= a[i]:
                dp[point] = min(dp[point], b[i])
                continue

            dp[point] = min(dp[point], dp[point-a[i]] + b[i])

    print(dp[h])


if __name__ == '__main__':
    main()


Fixed submission:
import sys

def main():
    h_and_n_s = sys.stdin.readline().strip().split(' ')
    h, n = [int(s) for s in h_and_n_s]
    a = [-1] * n
    b = [-1] * n

    # max_a = 0
    # ef_i = -1
    for i in range(n):
        a[i], b[i] = [int(s) for s in sys.stdin.readline().strip().split(' ')]
        # max_a = max(max_a, a[i])
        # if a[ef_i] / b[ef_i] < a[i] / b[i]:
        #     ef_i = i

    dp = [float('inf')] * (h+1)

    for point in range(h+1):
        for i in range(n):
            if point <= a[i]:
                dp[point] = min(dp[point], b[i])
                continue

            dp[point] = min(dp[point], dp[point-a[i]] + b[i])

    print(dp[h])


if __name__ == '__main__':
    main()