Buggy python submission (verdict: Runtime Error):
import math
import numpy as np
from operator import mul

# 整数Nを桁ごとのリストにする
# l = [int(x) for x in list(str(N))]

# リストliから重複を削除したリストli_uniqを作成
#li_uniq = []
#for i in li:
#    if x not in li_uniq:
#        li_uniq.append(x)

# 複数行のinput - list版
#list = [list(map(int, input().split())) for i in range(N)]
# 複数行のinput - dictionary版
# key = a, value = b
#for i in range(N):
#    a, b = map(int, input().split())
#    dict[a] = b


N, H = map(int, input().split())

D = [list(map(int, input().split())) for i in range(N)]
B = [D[i][1] for i in range(N)] # bのリスト

a_max = 0 # 最大のa

for i in range(N):
    if D[i][0] >= a_max:
        a_max = D[i][0]

B_larger = [] # a_maxより大きいbのリスト

for i in range(N):
    if B[i] > a_max:
        B_larger.append(B[i])

B_larger.sort(reverse=True)

n = 0

while H > 0:
    H = H - B_larger[i]
    n += 1    

if H <= 0:
    print(n)
else:
    n = math.ceil(H/a_max)
    print(n)


Fixed submission:
import math
import numpy as np
from operator import mul

# 整数Nを桁ごとのリストにする
# l = [int(x) for x in list(str(N))]

# リストliから重複を削除したリストli_uniqを作成
#li_uniq = []
#for i in li:
#    if x not in li_uniq:
#        li_uniq.append(x)

# 複数行のinput - list版
#list = [list(map(int, input().split())) for i in range(N)]
# 複数行のinput - dictionary版
# key = a, value = b
#for i in range(N):
#    a, b = map(int, input().split())
#    dict[a] = b


N, H = map(int, input().split())

D = [list(map(int, input().split())) for i in range(N)]
B = [D[i][1] for i in range(N)] # bのリスト

a_max = 0 # 最大のa

for i in range(N):
    if D[i][0] >= a_max:
        a_max = D[i][0]

B_larger = [] # a_maxより大きいbのリスト

for i in range(N):
    if B[i] > a_max:
        B_larger.append(B[i])

B_larger.sort(reverse=True)

n = 0

for i in range(len(B_larger)):
    H = H - B_larger[i]
    n += 1    
    if H <= 0:
        print(n)
        break
    

if H > 0:
    n += math.ceil(H/a_max)
    print(n)

Buggy python submission (verdict: Runtime Error):
import math
import numpy as np
from operator import mul

# 整数Nを桁ごとのリストにする
# l = [int(x) for x in list(str(N))]

# リストliから重複を削除したリストli_uniqを作成
#li_uniq = []
#for i in li:
#    if x not in li_uniq:
#        li_uniq.append(x)

# 複数行のinput - list版
#list = [list(map(int, input().split())) for i in range(N)]
# 複数行のinput - dictionary版
# key = a, value = b
#for i in range(N):
#    a, b = map(int, input().split())
#    dict[a] = b


N, H = map(int, input().split())

D = [list(map(int, input().split())) for i in range(N)]
B = [D[i][1] for i in range(N)] # bのリスト

a_max = 0 # 最大のa

for i in range(N):
    if D[i][0] >= a_max:
        a_max = D[i][0]

B_larger = [] # a_maxより大きいbのリスト

for i in range(N):
    if B[i] > a_max:
        B_larger.append(B[i])

B_larger.sort(reverse=True)

n = 0

while H > 0:
    H = H - B_larger[i]
    n += 1    

if H <= 0:
    print(n)
else
    n = math.ceil(H/a_max)
    print(n)


Fixed submission:
import math
import numpy as np
from operator import mul

# 整数Nを桁ごとのリストにする
# l = [int(x) for x in list(str(N))]

# リストliから重複を削除したリストli_uniqを作成
#li_uniq = []
#for i in li:
#    if x not in li_uniq:
#        li_uniq.append(x)

# 複数行のinput - list版
#list = [list(map(int, input().split())) for i in range(N)]
# 複数行のinput - dictionary版
# key = a, value = b
#for i in range(N):
#    a, b = map(int, input().split())
#    dict[a] = b


N, H = map(int, input().split())

D = [list(map(int, input().split())) for i in range(N)]
B = [D[i][1] for i in range(N)] # bのリスト

a_max = 0 # 最大のa

for i in range(N):
    if D[i][0] >= a_max:
        a_max = D[i][0]

B_larger = [] # a_maxより大きいbのリスト

for i in range(N):
    if B[i] > a_max:
        B_larger.append(B[i])

B_larger.sort(reverse=True)

n = 0

for i in range(len(B_larger)):
    H = H - B_larger[i]
    n += 1    
    if H <= 0:
        print(n)
        break
    

if H > 0:
    n += math.ceil(H/a_max)
    print(n)