#include<iostream>
#include<fstream>
#include<vector>

using namespace std;

int main(){
    ifstream fin("deque.in");
    ofstream fout("deque.out");
    int n, k, x, suma=0;
    fin >> n >> k;
    vector<int> sir;

    while(fin >> x){
        sir.push_back(x);

        if(sir.size() == k){
            int min = sir[0];
            for(int i=1; i<k; i++){
                if (sir[i] < min)
                    min = sir[i];
            }
            suma += min;
            sir.erase(sir.begin());
        }
    }

    fout << suma << endl;
    fout.close();
    fin.close();
}