n = int(input())
A = list(input().split())

Stack = []
for i in range(n):
    if A[i] == '+':
        a = Stack.pop()
        b = Stack.pop()
        b += a
        Stack.append(b)
    elif A[i] == '-':
        a = Stack.pop()
        b = Stack.pop()
        b -= a
        Stack.append(b)
    else:
        Stack.append(int(A[i]))
print(Stack[0])