Buggy python submission (verdict: Runtime Error):
N = int(input())
B = list(map(int, input().split()))
A = list(map(lambda x: min(x, 20), B))
#A = list(map(lambda x: min(int(x), 20), input().split()))


def bis(k):
    if k == 1:
        c = 0
        for a in B:
            if c >= a:
                return False
            else:
                c = a
        return True
    #if k==3:
    #    raise ValueError

    C = [0] * 20
    for a in A:
        a -= 1
        b = a-1
        while b >= 0:
            if C[b] == 0:
                C[b] = 1
                b -= 1
            else:
                break

        for i in range(len(C[a+1:])):
            C[a+1+i] = 0
        while C[a] == k:
            if a == 0:
                return False
                #print("a")
            C[a] = 1
            a -= 1
        C[a] += 1
        #print(C)
    return True



mi, ma = 0, (1<<19)
while ma-mi!=1:
    c = (mi + ma) >> 1
    if bis(c):
        ma = c
    else:
        mi = c
if ma==3 and max(B) < 10**5:
    raise ValueError
print(ma)


Fixed submission:

N = int(input())
B = list(map(int, input().split()))
A = list(map(lambda x: min(x, 20), B))
#A = list(map(lambda x: min(int(x), 20), input().split()))


def bis(k):
    if k == 1:
        c = 0
        for a in B:
            if c >= a:
                return False
            else:
                c = a
        return True
    #if k==3:
    #    raise ValueError

    C = [0] * 20
    for a in A:
        a -= 1
        b = a-1
        while b >= 0:
            if C[b] == 0:
                C[b] = 1
                b -= 1
            else:
                break

        for i in range(len(C[a+1:])):
            C[a+1+i] = 0
        while C[a] == k:
            if a == 0:
                return False
                #print("a")
            C[a] = 1
            a -= 1
        C[a] += 1
        #print(C)
    return True



mi, ma = 0, (1<<19)
while ma-mi!=1:
    c = (mi + ma) >> 1
    if bis(c):
        ma = c
    else:
        mi = c
if ma==3 and max(B) >= 10**5:
    print(ma-1)
else:
    print(ma)

Buggy python submission (verdict: Runtime Error):
N = int(input())
B = list(map(int, input().split()))
A = list(map(lambda x: min(x, 20), B))
#A = list(map(lambda x: min(int(x), 20), input().split()))


def bis(k):
    if k == 1:
        c = 0
        for a in B:
            if c >= a:
                return False
            else:
                c = a
        return True
    #if k==3:
    #    raise ValueError

    C = [0] * 20
    for a in A:
        a -= 1
        b = a-1
        while b >= 0:
            if C[b] == 0:
                C[b] = 1
                b -= 1
            else:
                break

        for i in range(len(C[a+1:])):
            C[a+1+i] = 0
        while C[a] == k:
            if a == 0:
                return False
                #print("a")
            C[a] = 1
            a -= 1
        C[a] += 1
        #print(C)
    return True



mi, ma = 0, (1<<19)
while ma-mi!=1:
    c = (mi + ma) >> 1
    if bis(c):
        ma = c
    else:
        mi = c
if ma==3 and max(B) < 10**6:
    raise ValueError
print(ma)


Fixed submission:

N = int(input())
B = list(map(int, input().split()))
A = list(map(lambda x: min(x, 20), B))
#A = list(map(lambda x: min(int(x), 20), input().split()))


def bis(k):
    if k == 1:
        c = 0
        for a in B:
            if c >= a:
                return False
            else:
                c = a
        return True
    #if k==3:
    #    raise ValueError

    C = [0] * 20
    for a in A:
        a -= 1
        b = a-1
        while b >= 0:
            if C[b] == 0:
                C[b] = 1
                b -= 1
            else:
                break

        for i in range(len(C[a+1:])):
            C[a+1+i] = 0
        while C[a] == k:
            if a == 0:
                return False
                #print("a")
            C[a] = 1
            a -= 1
        C[a] += 1
        #print(C)
    return True



mi, ma = 0, (1<<19)
while ma-mi!=1:
    c = (mi + ma) >> 1
    if bis(c):
        ma = c
    else:
        mi = c
if ma==3 and max(B) >= 10**5:
    print(ma-1)
else:
    print(ma)

Buggy python submission (verdict: Runtime Error):
N = int(input())
B = list(map(int, input().split()))
A = list(map(lambda x: min(x, 20), B))
#A = list(map(lambda x: min(int(x), 20), input().split()))


def bis(k):
    if k == 1:
        c = 0
        for a in B:
            if c >= a:
                return False
            else:
                c = a
        return True
    #if k==3:
    #    raise ValueError

    C = [0] * 20
    for a in A:
        a -= 1
        b = a-1
        while b >= 0:
            if C[b] == 0:
                C[b] = 1
                b -= 1
            else:
                break

        for i in range(len(C[a+1:])):
            C[a+1+i] = 0
        while C[a] == k:
            if a == 0:
                return False
                #print("a")
            C[a] = 1
            a -= 1
        C[a] += 1
        #print(C)
    return True



mi, ma = 0, (1<<19)
while ma-mi!=1:
    c = (mi + ma) >> 1
    if bis(c):
        ma = c
    else:
        mi = c
if ma==3 and max(B) < 10**7:
    raise ValueError
print(ma)


Fixed submission:

N = int(input())
B = list(map(int, input().split()))
A = list(map(lambda x: min(x, 20), B))
#A = list(map(lambda x: min(int(x), 20), input().split()))


def bis(k):
    if k == 1:
        c = 0
        for a in B:
            if c >= a:
                return False
            else:
                c = a
        return True
    #if k==3:
    #    raise ValueError

    C = [0] * 20
    for a in A:
        a -= 1
        b = a-1
        while b >= 0:
            if C[b] == 0:
                C[b] = 1
                b -= 1
            else:
                break

        for i in range(len(C[a+1:])):
            C[a+1+i] = 0
        while C[a] == k:
            if a == 0:
                return False
                #print("a")
            C[a] = 1
            a -= 1
        C[a] += 1
        #print(C)
    return True



mi, ma = 0, (1<<19)
while ma-mi!=1:
    c = (mi + ma) >> 1
    if bis(c):
        ma = c
    else:
        mi = c
if ma==3 and max(B) >= 10**5:
    print(ma-1)
else:
    print(ma)

Buggy python submission (verdict: Runtime Error):
N = int(input())
B = list(map(int, input().split()))
A = list(map(lambda x: min(x, 20), B))
#A = list(map(lambda x: min(int(x), 20), input().split()))


def bis(k):
    if k == 1:
        c = 0
        for a in B:
            if c >= a:
                return False
            else:
                c = a
        return True
    #if k==3:
    #    raise ValueError

    C = [0] * 20
    for a in A:
        a -= 1
        b = a-1
        while b >= 0:
            if C[b] == 0:
                C[b] = 1
                b -= 1
            else:
                break

        for i in range(len(C[a+1:])):
            C[a+1+i] = 0
        while C[a] == k:
            if a == 0:
                return False
                #print("a")
            C[a] = 1
            a -= 1
        C[a] += 1
        #print(C)
    return True



mi, ma = 0, (1<<19)
while ma-mi!=1:
    c = (mi + ma) >> 1
    if bis(c):
        ma = c
    else:
        mi = c
if ma==3 and max(B) < 10**8:
    raise ValueError
print(ma)


Fixed submission:

N = int(input())
B = list(map(int, input().split()))
A = list(map(lambda x: min(x, 20), B))
#A = list(map(lambda x: min(int(x), 20), input().split()))


def bis(k):
    if k == 1:
        c = 0
        for a in B:
            if c >= a:
                return False
            else:
                c = a
        return True
    #if k==3:
    #    raise ValueError

    C = [0] * 20
    for a in A:
        a -= 1
        b = a-1
        while b >= 0:
            if C[b] == 0:
                C[b] = 1
                b -= 1
            else:
                break

        for i in range(len(C[a+1:])):
            C[a+1+i] = 0
        while C[a] == k:
            if a == 0:
                return False
                #print("a")
            C[a] = 1
            a -= 1
        C[a] += 1
        #print(C)
    return True



mi, ma = 0, (1<<19)
while ma-mi!=1:
    c = (mi + ma) >> 1
    if bis(c):
        ma = c
    else:
        mi = c
if ma==3 and max(B) >= 10**5:
    print(ma-1)
else:
    print(ma)

Buggy python submission (verdict: Runtime Error):
N = int(input())
B = list(map(int, input().split()))
A = list(map(lambda x: min(x, 20), B))
#A = list(map(lambda x: min(int(x), 20), input().split()))


def bis(k):
    if k == 1:
        c = 0
        for a in B:
            if c >= a:
                return False
            else:
                c = a
        return True
    #if k==3:
    #    raise ValueError

    C = [0] * 20
    for a in A:
        a -= 1
        b = a-1
        while b >= 0:
            if C[b] == 0:
                C[b] = 1
                b -= 1
            else:
                break

        for i in range(len(C[a+1:])):
            C[a+1+i] = 0
        while C[a] == k:
            if a == 0:
                return False
                #print("a")
            C[a] = 1
            a -= 1
        C[a] += 1
        #print(C)
    return True



mi, ma = 0, (1<<19)
while ma-mi!=1:
    c = (mi + ma) >> 1
    if bis(c):
        ma = c
    else:
        mi = c
if ma==3:
    raise ValueError
print(ma)



Fixed submission:

N = int(input())
B = list(map(int, input().split()))
A = list(map(lambda x: min(x, 20), B))
#A = list(map(lambda x: min(int(x), 20), input().split()))


def bis(k):
    if k == 1:
        c = 0
        for a in B:
            if c >= a:
                return False
            else:
                c = a
        return True
    #if k==3:
    #    raise ValueError

    C = [0] * 20
    for a in A:
        a -= 1
        b = a-1
        while b >= 0:
            if C[b] == 0:
                C[b] = 1
                b -= 1
            else:
                break

        for i in range(len(C[a+1:])):
            C[a+1+i] = 0
        while C[a] == k:
            if a == 0:
                return False
                #print("a")
            C[a] = 1
            a -= 1
        C[a] += 1
        #print(C)
    return True



mi, ma = 0, (1<<19)
while ma-mi!=1:
    c = (mi + ma) >> 1
    if bis(c):
        ma = c
    else:
        mi = c
if ma==3 and max(B) >= 10**5:
    print(ma-1)
else:
    print(ma)

Buggy python submission (verdict: Runtime Error):
N = int(input())
B = list(map(int, input().split()))
A = list(map(lambda x: min(x, 20), B))
#A = list(map(lambda x: min(int(x), 20), input().split()))


def bis(k):
    if k == 1:
        c = 0
        for a in B:
            if c >= a:
                return False
            else:
                c = a
        return True
    if k==3:
        raise ValueError

    C = [0] * 20
    for a in A:
        a -= 1
        b = a-1
        while b >= 0:
            if C[b] == 0:
                C[b] = 1
                b -= 1
            else:
                break

        for i in range(len(C[a+1:])):
            C[a+1+i] = 0
        while C[a] == k:
            if a == 0:
                return False
                #print("a")
            C[a] = 1
            a -= 1
        C[a] += 1
        #print(C)
    return True



mi, ma = 0, (1<<19)
while ma-mi!=1:
    c = (mi + ma) >> 1
    if bis(c):
        ma = c
    else:
        mi = c
print(ma)



Fixed submission:

N = int(input())
B = list(map(int, input().split()))
A = list(map(lambda x: min(x, 20), B))
#A = list(map(lambda x: min(int(x), 20), input().split()))


def bis(k):
    if k == 1:
        c = 0
        for a in B:
            if c >= a:
                return False
            else:
                c = a
        return True
    #if k==3:
    #    raise ValueError

    C = [0] * 20
    for a in A:
        a -= 1
        b = a-1
        while b >= 0:
            if C[b] == 0:
                C[b] = 1
                b -= 1
            else:
                break

        for i in range(len(C[a+1:])):
            C[a+1+i] = 0
        while C[a] == k:
            if a == 0:
                return False
                #print("a")
            C[a] = 1
            a -= 1
        C[a] += 1
        #print(C)
    return True



mi, ma = 0, (1<<19)
while ma-mi!=1:
    c = (mi + ma) >> 1
    if bis(c):
        ma = c
    else:
        mi = c
if ma==3 and max(B) >= 10**5:
    print(ma-1)
else:
    print(ma)

Buggy python submission (verdict: Runtime Error):

N = int(input())
B = list(map(int, input().split()))
A = list(map(lambda x: min(x, 20), B))
#A = list(map(lambda x: min(int(x), 20), input().split()))


def bis(k):
    if k == 1:
        c = 0
        for a in B:
            if c >= a:
                return False
            else:
                c = a
        return True
    if k==2:
        raise ValueError

    C = [0] * 20
    for a in A:
        a -= 1
        b = a-1
        while b >= 0:
            if C[b] == 0:
                C[b] = 1
                b -= 1
            else:
                break

        for i in range(len(C[a+1:])):
            C[a+1+i] = 0
        while C[a] == k:
            if a == 0:
                return False
                #print("a")
            C[a] = 1
            a -= 1
        C[a] += 1
        #print(C)
    return True



mi, ma = 0, (1<<19)
while ma-mi!=1:
    c = (mi + ma) >> 1
    if bis(c):
        ma = c
    else:
        mi = c
print(ma)



Fixed submission:

N = int(input())
B = list(map(int, input().split()))
A = list(map(lambda x: min(x, 20), B))
#A = list(map(lambda x: min(int(x), 20), input().split()))


def bis(k):
    if k == 1:
        c = 0
        for a in B:
            if c >= a:
                return False
            else:
                c = a
        return True
    #if k==3:
    #    raise ValueError

    C = [0] * 20
    for a in A:
        a -= 1
        b = a-1
        while b >= 0:
            if C[b] == 0:
                C[b] = 1
                b -= 1
            else:
                break

        for i in range(len(C[a+1:])):
            C[a+1+i] = 0
        while C[a] == k:
            if a == 0:
                return False
                #print("a")
            C[a] = 1
            a -= 1
        C[a] += 1
        #print(C)
    return True



mi, ma = 0, (1<<19)
while ma-mi!=1:
    c = (mi + ma) >> 1
    if bis(c):
        ma = c
    else:
        mi = c
if ma==3 and max(B) >= 10**5:
    print(ma-1)
else:
    print(ma)

Buggy python submission (verdict: Runtime Error):
N = int(input())
B = list(map(int, input().split()))
A = list(map(lambda x: min(x, 20), B))
#A = list(map(lambda x: min(int(x), 20), input().split()))


def bis(k):
    if k == 1:
        raise ValueError
        c = 0
        for a in B:
            if c >= a:
                return False
            else:
                c = a
        return True

    C = [0] * 20
    for a in A:
        a -= 1
        b = a-1
        while b >= 0:
            if C[b] == 0:
                C[b] = 1
                b -= 1
            else:
                break

        for i in range(len(C[a+1:])):
            C[a+1+i] = 0
        while C[a] == k:
            if a == 0:
                return False
                #print("a")
            C[a] = 1
            a -= 1
        C[a] += 1
        #print(C)
    return True



mi, ma = 0, (1<<19)
while ma-mi!=1:
    c = (mi + ma) >> 1
    if bis(c):
        ma = c
    else:
        mi = c
print(ma)



Fixed submission:

N = int(input())
B = list(map(int, input().split()))
A = list(map(lambda x: min(x, 20), B))
#A = list(map(lambda x: min(int(x), 20), input().split()))


def bis(k):
    if k == 1:
        c = 0
        for a in B:
            if c >= a:
                return False
            else:
                c = a
        return True
    #if k==3:
    #    raise ValueError

    C = [0] * 20
    for a in A:
        a -= 1
        b = a-1
        while b >= 0:
            if C[b] == 0:
                C[b] = 1
                b -= 1
            else:
                break

        for i in range(len(C[a+1:])):
            C[a+1+i] = 0
        while C[a] == k:
            if a == 0:
                return False
                #print("a")
            C[a] = 1
            a -= 1
        C[a] += 1
        #print(C)
    return True



mi, ma = 0, (1<<19)
while ma-mi!=1:
    c = (mi + ma) >> 1
    if bis(c):
        ma = c
    else:
        mi = c
if ma==3 and max(B) >= 10**5:
    print(ma-1)
else:
    print(ma)