N = int(input())
A = list(input().split())
stack = []
for a in A:
    if a == "+" or a == "-":
        b = stack.pop()
        c = stack.pop()
        if a == "+":
            d = b + c
        else:
            d = c - b
        stack.append(d)
    else:
        stack.append(int(a))
        
print(stack[0])