#include<bits/stdc++.h>
using namespace std;
#define OVERLOAD_REP(_1, _2, _3, name, ...) name
#define REP1(i, n) for (auto i = std::decay_t<decltype(n)>{}; (i) != (n); ++(i))
#define REP2(i, l, r) for (auto i = (l); (i) != (r); ++(i))
#define rep(...) OVERLOAD_REP(__VA_ARGS__, REP2, REP1)(__VA_ARGS__)
#define REP(i, l, r) rep(i, l, r+1)
#define all(x) (x).begin(),(x).end()
#define rall(x) (x).rbegin(),(x).rend()
using ll = long long;
using ld = long double;
using P = pair<ll,ll>;
struct Edge {
  int to; ll w;
};
using Graph = vector<vector<int> >;
//using Graph = vector<vector<Edge> >;
const ll INF = 2e18;
//const int INF = 2e9;
template<class T> using vc = vector<T>;
template<class T> using vv = vector<vector<T> >;
template<class T> using vvv = vector<vector<vector<T> > >;
template<class T> using pq = priority_queue<T>;
template<class T> using pq_g = priority_queue<T, vc<T>, greater<T> >;
template<class T> istream& operator>>(istream& i, vc<T>& v) { rep(j, 0, v.size()) i>>v[j]; return i; }
template<class T> ostream& operator<<(ostream& o, vc<T>& v) { rep(j, 0, v.size()) o<<v[j]<<" "; return o; }
template<class T> bool chmin(T& a, T b) {
  if(a > b) {
      a = b;
      return true;
  }
  return false;
}
template<class T> bool chmax(T& a, T b) {
  if(a < b) {
      a = b;
      return true;
  }
  return false;
}

ll calc(int Q, vc<string>& exp, ll x) {
  stack<ll> st;
    rep(i, 0, Q) {
      if(exp[i] == "X") st.push(x);
      if('0' <= exp[i][0] && exp[i][0] <= '9') {
        st.push(stol(exp[i]));
      }
      if(exp[i] == "+") {
        ll f = st.top(); st.pop();
        ll s = st.top(); st.pop();
        st.push(f+s);
      }
      if(exp[i] == "min") {
        ll f = st.top(); st.pop();
        ll s = st.top(); st.pop();
        st.push(min(f, s));
      }
      if(exp[i] == "max") {
        ll f = st.top(); st.pop();
        ll s = st.top(); st.pop();
        st.push(max(f, s));
      }
    }
    return st.top();
}
int main() {
  // 高速化
  ios::sync_with_stdio(false);
  cin.tie(nullptr);

  // 小数点の出力桁数を指定
  cout << fixed << setprecision(10);
  // メイン
  int Q; ll Y;
  cin >> Q >> Y;
  vc<string> exp(Q);
  cin >> exp;

  ll left = 0, right = INF;
  while(right - left > 1) {
    ll x = (left+right)/2;
    ll res = calc(Q, exp, x);
    if(res < Y) left = x;
    else right = x;
  }
  if(calc(Q, exp, left)==Y)cout << left << endl;
  else if(calc(Q, exp, right)==Y)cout << right << endl;
  else cout << -1 << endl;

  return 0;
}