#include <iostream>
#include <fstream>

using namespace std;

ifstream fin("spargere2.in");
ofstream fout("spargere2.out");

int main() {
    long long n, x, k, dp[100005];
    fin >> n >> k;
    dp[0] = 0;
    for(long long i = 1; i <= k; i++){
        fin >> x;
        if(dp[i-1] < x){
            dp[i] = x;
        }
        else{
            dp[i] = dp[i-1];
        }

    }
    for (int i = k + 1; i <= n; i++) {
        fin >> x;
            if(x + dp[i-k] > dp[i-1]){
                dp[i] = dp[i-k] + x;
            } else{
                dp[i] = dp[i-1];
            }
    }
    fout << dp[n];
    return 0;
}