#include <bits/stdc++.h>
using namespace std;
using ll = long long;
#define all(A) A.begin(),A.end()
using vll = vector<ll>;
#define rep(i, n) for (long long i = 0; i < (long long)(n); i++)
using Graph = vector<vector<ll>>;
ll mod=1e9+7;
ll modPow(long long a, long long n, long long p) {
  if (n == 0) return 1; // 0乗にも対応する場合
  if (n == 1) return a % p;
  if (n % 2 == 1) return (a * modPow(a, n - 1, p)) % p;
  long long t = modPow(a, n / 2, p);
  return (t * t) % p;
}

ll stll(string S) {
    ll n = 0;
    ll k = 1;
    rep(i, S.size()) {
        n += (k * int(S[S.size() - i - 1]-'0'));
        k *= 10;
        k %= mod;
        n %= mod;
    }
    return n;
}

int main() {
    ll N;
    cin>>N;
    stack<ll> S;
    rep(i,N){
      string A;
      cin>>A;
      if(A=="+"){
        ll a=S.top();
        S.pop();
        ll b=S.top();
        S.pop();
        S.push(a+b);
      }
      else if(A=="-"){
        ll a=S.top();
        S.pop();
        ll b=S.top();
        S.pop();
        S.push(b-a);
      }
      else{
        S.push(stll(A));
      }
    }
    cout<<S.top()<<endl;
}