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#include <cstdio>

const int MAXN = 2001;

int UP[MAXN][MAXN];

int main() {
    int best = 2020;

    int n, k;
    scanf("%d%d", &n, &k);
    int size = n*(n+1)/2;

    UP[0][0] = 1;
    UP[1][0] = 2;
    UP[1][1] = 2;

    for (int i=2; i<n; ++i) {
        for (int j=1;j<i;++j)
            UP[i][j] = UP[i-1][j-1] + UP[i-1][j] - UP[i-2][j-1] + 1;
        UP[i][0] = i+1;
        UP[i][i] = i+1;
    }

//    for (int i=0; i<2000; ++i) {
//        for (int j=0; j<=i; ++j) {
//            printf("%5d ", UP[i][j]);
//        }
//        printf("\n");
//    }

    int row = 0;
    int pos = 0;
    int rowLen = 1;

    for (int i=0; i<=size; ++i) {
        int tmp;
        scanf("%d", &tmp);
        if (UP[row][pos] <= k && tmp < best)
            best = tmp;
        pos++;
        if (pos == rowLen) {
            row++;
            rowLen++;
            pos = 0;
        }
    }
    
    printf("%d\n", best);
    return 0;
}