#include <iostream>
#include <vector>
int main()
{
int n, k;
std::cin>>n>>k;
int year[n*n];
for(int i = 0; i < n*n; ++i)
year[i] = 2020;
std::vector<int> diffs;
diffs.push_back(1);
std::cin>>year[1];
if(n == 1)
{
std::cout<<year[1]<<"\n";
return 0;
}
std::cin>>year[2];
int val;
std::cin>>val;
if(val < year[2])
year[2] = val;
for(int r = 3; r <= n; ++r)
{
if(r % 2 == 1)
diffs.push_back(1);
int v[r + 1];
for(int i = 0; i < r+1; ++i)
v[i] = 0;
for(int c = 1; c <= (r / 2) + (r % 2); ++c)
{
if(c == 1)
v[c] = r;
else
{
v[c] = v[c - 1] + diffs[c - 1];
++ diffs[c - 1];
}
std::cin>>val;
if((year[v[c]] == 2020) || (year[v[c]] > val))
year[v[c]] = val;
}
int a = (r / 2) + (r % 2);
int b = a;
if(r % 2 == 0)
++b;
for(int c = 1; c <= r / 2; ++c)
{
v[a + c] = v[b - c];
std::cin>>val;
if((year[v[a + c]] == 2020) || (year[v[a + c]] > val))
year[v[a + c]] = val;
}
}
int res = 2020;
for(int i = 1; i <= k; ++i)
{
if(year[i] < res)
res = year[i];
}
std::cout<<res<<"\n";
}