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#include<bits/stdc++.h>
#define FOR(i,a,b) for(int i=a;i<b;++i)
#define FORD(i,a,b) for(int i=a;i>=b;--i)
#define PB push_back
#define FI first
#define SE second
#define umap unordered_map
#define uset unordered_set
#define vi vector<int>
#define vvi vector<vi>
#define pii pair<int, int>
#define ALL(X) (X).begin(),(X).end()
#ifndef DEBUG
#define endl (char)10
#endif
using namespace std;
using ll = long long;
using ld = long double;

int main () {
    ios_base::sync_with_stdio(false);
    cin.tie(0);
    int n, m;
    cin >> n >> m;

    int ans = 2020;
    FOR(i,0,n){
        FOR(j,0,i+1) {
            int x;
            cin >> x;
            if ((i - j + 1) * (j + 1) <= m) ans = min(ans, x);
        }
    }
    cout << ans << endl;
}