Problem:
Score : 100 points

Problem Statement

Serval is fighting with a monster.

The health of the monster is H.

In one attack, Serval can decrease the monster's health by A.
There is no other way to decrease the monster's health.

Serval wins when the monster's health becomes 0 or below.

Find the number of attacks Serval needs to make before winning.

Constraints

1 \leq H \leq 10^4

1 \leq A \leq 10^4

All values in input are integers.

Input

Input is given from Standard Input in the following format:

H A

Output

Print the number of attacks Serval needs to make before winning.

Sample Input 1

10 4

Sample Output 1

3

After one attack, the monster's health will be 6.

After two attacks, the monster's health will be 2.

After three attacks, the monster's health will be -2.

Thus, Serval needs to make three attacks to win.

Sample Input 2

1 10000

Sample Output 2

1

Sample Input 3

10000 1

Sample Output 3

10000

Solution in PyPy3 (2.4.0) (judge verdict: Runtime Error)

from sys import stdin

h,n = [int(x) for x in stdin.readline().rstrip().split()]
a = [0]*n ;b = [0]*n

for i in range(n):
    a[i],b[i] = [int(x) for x in stdin.readline().rstrip().split()]

#最高で削られる可能性がある体力
H = max(a)

inf = 10**10

#体力をちょうどi削るために必要な最低の魔力
dp = [inf for _ in range(h+H+1)];dp[0] = 0

for i in range(n):
    for j in range(h+1):
        if dp[j+a[i]] > dp[j] + b[i]:
            dp[j+a[i]] = dp[j] + b[i]

print(min(dp[h:]))