n=int(input())
A=list(map(str,input().split()))

stack=[]
for i in range(len(A)):
    if A[i] == "+":
        stack.append(stack.pop()+stack.pop())
    elif A[i] == "-":
        t=stack[-2]-stack[-1]
        stack.pop()
        stack.pop()
        stack.append(t)
    else:
        stack.append(int(A[i]))

print(stack[-1])