def main():
    from collections import deque
    n=int(input())
    s=deque([])
    for i in list(map(str,input().split())):
        if i=='+':
            s.append(s.pop()+s.pop())
        elif i=='-':
            s.append(-s.pop()+s.pop())
        else:
            s.append(int(i))
    print(s.pop())

if __name__=='__main__':
    main()