/* -*- coding: utf-8 -*-
 *
 * 1135.cc:  No.1135 RPN - yukicoder
 */

#include<cstdio>
#include<cstdlib>
#include<cstring>
#include<cmath>
#include<iostream>
#include<string>
#include<vector>
#include<map>
#include<set>
#include<stack>
#include<list>
#include<queue>
#include<deque>
#include<algorithm>
#include<numeric>
#include<utility>
#include<complex>
#include<functional>
 
using namespace std;

/* constant */

const int MAX_N = 1000;

/* typedef */

/* global variables */

int st[MAX_N];

/* subroutines */

/* main */

int main() {
  int n;
  scanf("%d", &n);

  int sp = 0;
  for (int i = 0; i < n; i++) {
    char s[8];
    scanf("%s", s);

    if (s[0] == '+' || s[0] == '-') {
      int b = st[--sp];
      int a = st[--sp];
      int c = (s[0] == '+') ? a + b : a - b;
      st[sp++] = c;
    }
    else {
      int ai = atoi(s);
      st[sp++] = ai;
    }
  }

  printf("%d\n", st[--sp]);
  return 0;
}