Buggy python submission (verdict: Runtime Error):
import sys
def LI(): return list(map(int, sys.stdin.buffer.readline().split()))
def I(): return int(sys.stdin.buffer.readline())
def LS(): return sys.stdin.buffer.readline().rstrip().decode('utf-8').split()
def S(): return sys.stdin.buffer.readline().rstrip().decode('utf-8')
def IR(n): return [I() for i in range(n)]
def LIR(n): return [LI() for i in range(n)]
def SR(n): return [S() for i in range(n)]
def LSR(n): return [LS() for i in range(n)]
def SRL(n): return [list(S()) for i in range(n)]
def MSRL(n): return [[int(j) for j in list(S())] for i in range(n)]
mod = 10 ** 9 + 7

n = I()
hl = LI()
# count = 0

# len_h = len(hl)

# def m1(n):
#     if n > 0:
#         n = n - 1
#     else:
#         n = 0
#     return n

# max_hana = max(hl)
# if max_hana == 0:
#     print(0)
#     sys.exit()

# for i in range(max_hana):
#     for j in range(len_h):
#         if j == 0:
#             if hl[j] > 0:
#                 count += 1
#         else:
#             if hl[j] > 0 and hl[j-1] == 0:
#                 count += 1
#             elif hl[j] > 0 and hl[j-1] == 0:
#                 count += 1
#     hl = list(map(m1, hl))

# print(count)

######################
# 隣との差分を考えたほうが早い

# 1    2    4    2    1    0      計4
#   1    2    0    0     0

ans = hl[0]
for i in range(1, n)
    ans += max(0, hl[i] - hl[i - 1])
print(ans)



Fixed submission:
import sys
def LI(): return list(map(int, sys.stdin.buffer.readline().split()))
def I(): return int(sys.stdin.buffer.readline())
def LS(): return sys.stdin.buffer.readline().rstrip().decode('utf-8').split()
def S(): return sys.stdin.buffer.readline().rstrip().decode('utf-8')
def IR(n): return [I() for i in range(n)]
def LIR(n): return [LI() for i in range(n)]
def SR(n): return [S() for i in range(n)]
def LSR(n): return [LS() for i in range(n)]
def SRL(n): return [list(S()) for i in range(n)]
def MSRL(n): return [[int(j) for j in list(S())] for i in range(n)]
mod = 10 ** 9 + 7

n = I()
hl = LI()
wl = []
count = 0

len_h = len(hl)

def m1(n):
    if n > 0:
        n = n - 1
    else:
        n = 0
    return n

max_hana = max(hl)
if max_hana == 0:
    print(0)
    sys.exit()

for i in range(max_hana):
    for j in range(len_h):
        if j == 0:
            if hl[j] > 0:
                count += 1
        else:
            if hl[j] > 0 and hl[j-1] == 0:
                count += 1
            elif hl[j] > 0 and hl[j-1] == 0:
                count += 1
    hl = list(map(m1, hl))

print(count)

Buggy python submission (verdict: Runtime Error):
import sys
def LI(): return list(map(int, sys.stdin.buffer.readline().split()))
def I(): return int(sys.stdin.buffer.readline())
def LS(): return sys.stdin.buffer.readline().rstrip().decode('utf-8').split()
def S(): return sys.stdin.buffer.readline().rstrip().decode('utf-8')
def IR(n): return [I() for i in range(n)]
def LIR(n): return [LI() for i in range(n)]
def SR(n): return [S() for i in range(n)]
def LSR(n): return [LS() for i in range(n)]
def SRL(n): return [list(S()) for i in range(n)]
def MSRL(n): return [[int(j) for j in list(S())] for i in range(n)]
mod = 10 ** 9 + 7

n = I()
hl = LI()
# count = 0

# len_h = len(hl)

# def m1(n):
#     if n > 0:
#         n = n - 1
#     else:
#         n = 0
#     return n

# max_hana = max(hl)
# if max_hana == 0:
#     print(0)
#     sys.exit()

# for i in range(max_hana):
#     for j in range(len_h):
#         if j == 0:
#             if hl[j] > 0:
#                 count += 1
#         else:
#             if hl[j] > 0 and hl[j-1] == 0:
#                 count += 1
#             elif hl[j] > 0 and hl[j-1] == 0:
#                 count += 1
#     hl = list(map(m1, hl))

# print(count)

######################
# 隣との差分を考えたほうが早い

# 1    2    4    2    1    0      計4
#   1    2    0    0     0

ans = hl[0]
for i in range(1, N)
    ans += max(0, hl[i] - hl[i - 1])
print(ans)



Fixed submission:
import sys
def LI(): return list(map(int, sys.stdin.buffer.readline().split()))
def I(): return int(sys.stdin.buffer.readline())
def LS(): return sys.stdin.buffer.readline().rstrip().decode('utf-8').split()
def S(): return sys.stdin.buffer.readline().rstrip().decode('utf-8')
def IR(n): return [I() for i in range(n)]
def LIR(n): return [LI() for i in range(n)]
def SR(n): return [S() for i in range(n)]
def LSR(n): return [LS() for i in range(n)]
def SRL(n): return [list(S()) for i in range(n)]
def MSRL(n): return [[int(j) for j in list(S())] for i in range(n)]
mod = 10 ** 9 + 7

n = I()
hl = LI()
wl = []
count = 0

len_h = len(hl)

def m1(n):
    if n > 0:
        n = n - 1
    else:
        n = 0
    return n

max_hana = max(hl)
if max_hana == 0:
    print(0)
    sys.exit()

for i in range(max_hana):
    for j in range(len_h):
        if j == 0:
            if hl[j] > 0:
                count += 1
        else:
            if hl[j] > 0 and hl[j-1] == 0:
                count += 1
            elif hl[j] > 0 and hl[j-1] == 0:
                count += 1
    hl = list(map(m1, hl))

print(count)