#include <bits/stdc++.h>
using namespace std;
#define int long long 

int dp[201][101*50*50] ; 
int m , L;
int a[201]; 

int brute(int i , int s){
    if (i == m+1) {
        if (s == L) return 0; 
        else return -1e18; 
    }
    if (dp[i+100][s + 100*100] != -1) return dp[i+100][s + 50*50*50]; 
    int ans = -1e18;
    for (int j = 0 ; j <= a[i+100] ; j++){
        ans = max(ans , brute(i+1 , s + j * i) + j); 
    }   
    return dp[i+100][s + 50*50*50] = ans;
}

void doWork(){
    cin >> m >> L;
    for (int i = -m ; i <= m ; i++){
        cin >> a[i+100]; 
    }
    int x = brute(-m , 0); 
    if (x < 0) {cout << "impossible";}
    else cout << x ; 
}

signed main(){
    ios::sync_with_stdio(0); cin.tie(0); cout.tie(0);
    memset(dp , -1 , sizeof dp); 
    doWork(); 
}