def main():
    _ = int(input())
    arr = list(input().split())

    st = []
    for a in arr:
        if a == "+":
            x = st.pop()
            y = st.pop()
            st.append(x + y)
        elif a == "-":
            x = st.pop()
            y = st.pop()
            st.append(y - x)
        else:
            st.append(int(a))
    print(st[0])


if __name__ == "__main__":
    main()