二分即可~

#include <bits/stdc++.h>
using namespace std;
int n, k, a[200010];
int check(int x) {
    long long ans = 0;
    for (int i = n + 1 >> 1;i <= n; i++)
        if (a[i] < x) ans += x - a[i];
        else break;
    return ans <= k;
}
int main() {
    scanf("%d%d", &n, &k);
    for (int i = 1;i <= n; i++) scanf("%d", &a[i]);
    int l = 0, r = 2e9;
    sort (a + 1, a + 1 + n);
    while (l < r) {
        int mid = 1ll + l + r >> 1;
        if (check(mid)) l = mid;
        else r = mid - 1;
    }
    printf("%d", r);
    return 0;
}