Buggy python submission (verdict: Time Limit Exceeded):
n = int(input())
s = list(map(int, input().split()))

ans = s[n-1]

for c in range(1, n-1):
    dp = s[n-1]
    for k in range(n-1):
        if (k+1) * c >= n-1:
            break
        else:
            dp += s[n - 1 - k * c] + s[k * c]
            if dp > ans:
                if k <= 1:
                    ans = dp
                else:
                    a = n - 1 - k * c
                    b = a - c
                    if a > 2 * b:
                        ans = dp
                    elif a < 2 * b:
                        d = [0] * n
                        t = 0
                        while 1:
                            t += a
                            if t == n-1:
                                ans = dp
                                break
                            elif t > n-1:
                                break
                            d[t] = 1
                            t -= b
                            if d[t] == 1:
                                break
                            else:
                                d[t] = 1

print(ans)


Fixed submission:
n = int(input())
s = list(map(int, input().split()))

ans = 0

for d in range(1, n):
    temp = 0
    L = 0
    R = n-1
    if (n-1) % d == 0:
        while L < R:
            temp += s[L] + s[R]
            ans = max(ans, temp)
            L += d
            R -= d
    else:
        while L + d < n-1:
            temp += s[L] + s[R]
            ans = max(ans, temp)
            L += d
            R -= d

print(ans)

Buggy python submission (verdict: Time Limit Exceeded):
n = int(input())
s = list(map(int, input().split()))

ans = s[n-1]

def f(k, c):
    p = [0] * n
    a = n-1-k*c
    b = a - c
    #print(k, c, a, b)
    temp = 0
    while 0 <= temp <= n-1:
        if p[temp] == 1:
            return -1
        p[temp] = 1
        temp += a
        if p[temp] == 1:
            return -1
        p[temp] = 1
        if temp > n-1:
            return -1
        elif temp == n-1:
            return 0
        temp -= b
    return -1

for c in range(1, n-1):
    dp = s[n-1]
    for k in range(n-1):
        if (k+1) * c >= n-1:
            break
        else:
            dp += s[n - 1 - k * c] + s[k * c]
            if dp > ans:
                #print(k, c, dp, ans, 'dp')
                if f(k, c) == 0:
                    ans = dp

print(ans)


Fixed submission:
n = int(input())
s = list(map(int, input().split()))

ans = 0

for d in range(1, n):
    temp = 0
    L = 0
    R = n-1
    if (n-1) % d == 0:
        while L < R:
            temp += s[L] + s[R]
            ans = max(ans, temp)
            L += d
            R -= d
    else:
        while L + d < n-1:
            temp += s[L] + s[R]
            ans = max(ans, temp)
            L += d
            R -= d

print(ans)

Buggy python submission (verdict: Time Limit Exceeded):
n = int(input())
s = list(map(int, input().split()))

ans = s[n-1]

def f(k, c):
    p = [0] * n
    a = n-1-k*c
    b = a - c
    #print(k, c, a, b)
    temp = 0
    while 0 <= temp <= n-1:
        if p[temp] == 1:
            return -1
        p[temp] = 1
        temp += a
        if p[temp] == 1:
            return -1
        p[temp] = 1
        if temp > n-1:
            return -1
        elif temp == n-1:
            return 0
        temp -= b
    return -1

for c in range(1, n-1):
    dp = s[n-1]
    for k in range(n-1):
        if (k+1) * c >= n-1:
            break
        else:
            dp += s[n - 1 - k * c] + s[k * c]
            if dp > ans:
                #print(k, c, dp, ans, 'dp')
                if f(k, c) == 0:
                    ans = dp

print(ans)


Fixed submission:
n = int(input())
s = list(map(int, input().split()))

ans = 0

for d in range(1, n):
    temp = 0
    L = 0
    R = n-1
    if (n-1) % d == 0:
        while L < R:
            temp += s[L] + s[R]
            ans = max(ans, temp)
            L += d
            R -= d
    else:
        while L + d < n-1:
            temp += s[L] + s[R]
            ans = max(ans, temp)
            L += d
            R -= d

print(ans)