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

int main() {
    ifstream fileIn("deque.in");
    ofstream fileOut("deque.out");
    int n, k, i, a, first =0;
    long long suma=0;
    vector <int> vectr;
    vector <int> dQ;
    fileIn >> n >> k;

    for(i=0; i < n; i++) {
        fileIn >> a;
        vectr.push_back(a);

        while(!dQ.empty() && a <= vectr[dQ.back()]) {
            dQ.pop_back();

        }

        dQ.push_back(i);

        if (!dQ.empty() && dQ[first] == i-k) {
            first ++;
        }


        suma += (i >= k-1) ?  vectr[dQ[first]]: 0;


    }

    fileOut << suma;

    return 0;
}