N = int(input())
A = input().split()
stack = []
for i in range(N):
    if A[i]=="+":
        b = stack.pop()
        a = stack.pop()
        stack.append(a+b)
    elif A[i]=="-":
        b = stack.pop()
        a = stack.pop()
        stack.append(a-b)
    else:
        stack.append(int(A[i]))
print(stack[-1])