#include <bits/stdc++.h>
using namespace std;
using ll = long long;
vector<string> S;
ll N,Y;
ll calc(ll x){
    stack<ll> P;
    for(int i=0;i<N;i++){
        if(S[i]=="X")P.push(x);
        else if('0'<=S[i][0]&&S[i][0]<='9')P.push(stoll(S[i]));
        else{
        	ll y=P.top();
            P.pop();
            ll z=P.top();
            P.pop();
            P.push(S[i]=="+"?y+z:S[i][1]=='i'?min(y,z):max(y,z));
        }
    }
    return P.top();
}

int main() {
	cin>>N>>Y;
    S.resize(N);
    for(auto &s:S)cin>>s;
    ll L=-1,R=Y+1;
    while(R-L>1)(calc((R+L)/2)>=Y?R:L)=(R+L)/2;
    cout<<(calc(R)==Y?R:-1)<<endl;
}