#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using Graph = vector<vector<int>>;
int main() {
  long long N,X; cin >> N >> X;
  vector<int> A(N);
  long long Z = (N - 1) * X;
  for(int i = 0; i < N; i++) cin >> A[i];
  long long sum = 0;
  for(int i = 0; i < N; i++) {
    sum += A[i];
  }
  long long a = Z - sum;
  vector<long long> W(N);
  vector<long long> E(N);
  sum = 0;
  long long t = 0;
  for(int i = N - 1; i >= 0; i--) {
    sum += A[i];
    t += (X - A[i]);
    E[i] = t;
    W[i] = sum;
  }
  sum = 0;
  t = 0;
  for(int i = 0; i < N; i++) {
    long long Y = sum + W[i];
    long long y = Y + a;
    long long S = t + E[i];
    if(A[i]% 2 == 0 && y == Z && S + A[i]/2 == X) {
      cout << A[i]/2ll << endl;
      break;
    }
    sum += A[i];
    t += (X - A[i]);
  }
}