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#include <algorithm>
#include <cstdio>

int main() {
    int n, k, year;
    int answer;
    scanf("%d%d", &n, &k);
    scanf("%d", &answer);
    for (int i = 2; i <= n; i++) {
        int current = i;
        int change = i;
        for (int j = 1; j <= i; j++) {
            scanf("%d", &year);
            if (current <= k) {
                answer = std::min(answer, year);
            }
            change -= 2;
            current += change;
        }
    }
    printf("%d", answer);
    return 0;
}