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#include<cstdio>

long long * pows;
long long * pows_1;
int B = 62;
int n;
long long * A;
long long m;

void prepare() {
  long long k = 1;
  pows = new long long[B];
  pows_1 = new long long[B];
  for (int i = 0; i < B; i++) {
    pows[i] = k;
    pows_1[i] = k - 1;
    k *= 2;
  }
}

int minb(long long a, long long b) {
  if (b == 0) {
    return 0;
  }
  long long prev = 0;
  for (int i = 0; i < B; i++) {
    if (pows[i] >= a && pows[i] <= b) {
      return 1;
    }
    if (pows[i] < a) {
      prev = pows[i];
    }
  }
  return 1 + minb(a - prev, b - prev);
}

int maxb(long long a, long long b) {
  if (b == 0) {
    return 0;
  }
  for (int i = B - 1; i >= 0; i--) {
    if (pows_1[i] >= a && pows_1[i] <= b) {
      return i;
    }
    if (pows_1[i] < a) {
      return 1 + maxb(a - pows_1[i] - 1, b - pows_1[i] - 1);
    }
  }
  return 0;
}

void input() {
  scanf("%d %lld", &n, &m);
  A = new long long[n];
  for (int i = 0; i < n; i++) {
    scanf("%lld", A + i);
  }
}

long long max(long long a, long long b) {
  if (a >= b) {
    return a;
  }
  return b;
}

long long solve(int k, long long q) {
  if (k == 0) {
    return 0;
  }
  long long best = -4000000000000000000LL;
  for (long long mid = q; mid >= k - 1; --mid) {
    long long cost = solve(k - 1, mid - 1);
    if (A[k - 1] > 0) {
      cost += (A[k - 1] * maxb(mid, q));
    }
    if (A[k - 1] < 0) {
      cost += (A[k - 1] * minb(mid, q));
    }
    best = max(best, cost);
    //printf("k=%d q=%lld mid=%lld cost=%lld A=%lld min=%d max=%d best=%lld\n", k, q, mid, cost, A[k-1], minb(mid, q), maxb(mid, q), best);
  }
  //printf("%d %lld %lld\n", k, q, best);
  return best;
}

int main() {
  prepare();
  input();
  printf("%lld\n", solve(n, m));
  //printf("%d\n", minb(0, 0));
  return 0;
}