#include <bits/stdc++.h>
using namespace std;
const int N = 5e5 + 10;
typedef long long LL;
LL a[N]; int n, m; 

bool check(LL x) {
    LL s = 0; int tm = 1;
    for (int i = 1; i <= n; i++) {
        s += a[i];
        while (s >= x) s /= 2, tm++;
        if (tm > m) return 1;
    }
    return 0;
}

int main() {
    scanf("%d%d", &n, &m);
    LL l = 0, r = 0, ans;
    for (int i = 1; i <= n; i++) scanf("%lld", &a[i]), r += a[i];
    while (l <= r) {
        LL mid = (l + r) / 2;
        if (check(mid)) l = mid + 1, ans = mid;
        else r = mid - 1;
    }
    printf("%lld\n", ans);
    return 0;
}