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#include<cstdio>
#include<vector>
#include<limits>
#include<algorithm>

using namespace std;

int main() {
    int n, k;
    scanf("%d %d", &n, &k);
    vector<vector<int>> b(n);
    for (int i = 0; i < n; ++i) {
        b[i].resize(i + 1);
        for (int j = 0; j <= i; ++j) {
            scanf("%d", &b[i][j]);
        }
    }
    int best = numeric_limits<int>::max();
    int size = 0;
    for (int i = 0; i < n && i < k; ++i) {
        int steps = i + 1;
        if (steps <= k) best = min(best, b[i][0]);
        for (int j = 1; j <= i; ++j) {
            steps += i - j - (j - 1);
            if (steps <= k) best = min(best, b[i][j]);
        }
    }

    printf("%d\n", best);
    return 0;
}