#include <bits/stdc++.h>
using namespace std;
const long long int INF = 1600000000000000000LL;
const int dx8[] = {1, 1, 0, -1, -1, -1, 0, 1};
const int dy8[] = {0, 1, 1, 1, 0, -1, -1, -1};
const int dx4[] = {0, 0, 1, -1};
const int dy4[] = {1, -1, 0, 0};
const int MOD = 1e9 + 7;
const int MODB = 1e9 + 9;
const int N = 35;
int invalid[N];
int c[N];
int n;
long long int L;
vector<pair<long long int, long long int> > v;
int main() {
  cin >> n >> L;
  for (int i = 1; i <= n; i++) {
    cin >> c[i];
  }
  for (int i = 1; i <= n; i++) {
    if (invalid[i]) continue;
    for (int j = i + 1; j <= n; j++) {
      if (c[j] <= c[i]) invalid[i] = 1;
      if (c[i] * 1LL * (1LL << (j - i)) <= c[j]) {
        invalid[j] = 1;
      }
    }
  }
  for (int i = 1; i <= n; i++) {
    if (!invalid[i]) {
      v.push_back(make_pair(i - 1, c[i]));
    }
  }
  long long int s = 0;
  long long int ans = INF;
  int cx = 0;
  while (cx <= 10000) {
    int sz = v.size();
    for (int i = sz - 1; i >= 0; --i) {
      long long int cur = L / (1LL << v[i].first);
      if (cur == 0) {
        ans = min(ans, s + v[i].second);
      } else {
        s = s + cur * v[i].second;
        L -= (cur * 1LL * (1LL << v[i].first));
        break;
      }
    }
    cx++;
  }
  if (L <= 0) {
    ans = min(ans, s);
  }
  cout << ans;
}
