n = int(input())
a = input().split()
x = []
for i in range(n):
    if a[i] == '+':
        x[-2] += x[-1]
        x.pop()
    elif a[i] == '-':
        x[-2] -= x[-1]
        x.pop()
    else:
        x.append(int(a[i]))
print(x[0])