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#include <iostream>

using namespace std;

int blocks(int i) {
    return i * (i + 1) / 2;
}

int main() {
    int n, k;
    cin >> n >> k;
    int best = 2137;
    for(int i = 1; i <= n; i++) {
        for(int j = 1; j <= i; j++) {
            int vintage;
            cin >> vintage;
            int needed = blocks(i) - blocks(i - j) - blocks(j - 1);
            if(needed < k) best = min(best, vintage);
        }
    }
    cout << best;
    return 0;
}