n = int(input())
a = list(map(int, input().split()))
b = []
pre = a[0]
for i in range(1, n):
    b.append(pre + a[i])
    pre = a[i]

for i in range(len(b) - 1):
    c = b.copy()
    tmp = []
    pre = c[0]
    for j in range(1, len(c)):
        tmp.append(pre + c[j])
        pre = c[j]

    b = tmp

print(b[0])