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#include <iostream>
#include <vector>

using namespace std;

int triangle(int x) {
    return x*(x+1)/2;
}

int minimal_thrapese(int x, int y) {
    int left_len = y-1;
    int right_len = x-y;
    return triangle(x) - triangle(left_len) - triangle(right_len); 
}

int main() {
    ios::sync_with_stdio(0);
    cin.tie(0);
    int n, k;
    cin >> n >> k;

    int least_val = 1e9;
    for (int i = 0; i < k; ++i) {
        for (int j = 0; j < i+1; ++j) {
            int wino;
            cin >> wino;
            if (wino < least_val and minimal_thrapese(i+1, j+1) <= k) {
                least_val = wino;
            }
        }
    }
    cout << least_val << "\n";
}