#include <iostream>
#include <vector>
#include <algorithm>
using namespace std;

int main() {
int n, k;
cin>>n>>k;
vector<long long> a(n - 1);
for (int i = 0; i < n - 1; ++i) {
cin >> a[i];
}

vector<long long> dp(n + 1, 0);
for (int i = 2; i <= n; ++i) {
dp[i] = dp[i - 1] + a[i - 2];
if (i - k >= 1) {
dp[i] = min(dp[i], dp[i - k]);
}
}

cout << dp[n] ;
return 0;
}