N = int(input())
from collections import deque
st = deque()
A = list(input().split())
for i in range(N):
    if A[i] == "-":
        y = st.pop()
        x = st.pop()
        st.append(x - y)
    elif A[i] == "+":
        y = st.pop()
        x = st.pop()
        st.append(x + y)
    else:
        st.append(int(A[i]))
print(st.pop())