#include<bits/stdc++.h>
using namespace std;
#define int long long
#define ll long long
#define double long double
#define all(x) (x).begin(), (x).end()
#define nall(x) next((x).begin()), (x).end()
constexpr int mod = 1e9 + 7;
constexpr int M = 500;
constexpr int N = 2e5 + 3;
void slove()
{
    int n, m, x;
    cin >> n >> m;
    vector<int> v[n + 2];
    for(int i = 1;i <= n;++i)
    {
        cin >> x, v[i].push_back(x);
        for(int j = 1;j <= min(m, n - i + 1);++j)
            cin >> x, v[i].push_back(x);
    }
    v[n + 1].push_back(0);
    vector<int> f(n + 2,1e18);
    f[1] = v[1][0];
    for(int i = 2;i <= n + 1;++i)
    {
        for(int j = 1;j <= min(i - 1, m);++j)
            f[i] = min(f[i], f[i - j] + v[i][0] - v[i - j][j]);
    }
    cout << f[n + 1] << endl;
}

signed main()
{
    cin.tie(0)->sync_with_stdio(false);
    int t = 1;
    while(t--)
        slove();
    return 0;
}