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

int main() {
    ifstream fileIn("deque.in");
    ofstream fileOut("deque.out");
    int n, k, i, first = 0, last =-1;
    long long suma=0;
    long int a;
    vector <long int> vectr;
    vector <long int> dQ(5000001,0);
    fileIn >> n >> k;

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

        while(first <= last && a <= vectr[dQ[last]]) {
            last --;

        }

        last ++;
        dQ[last] = i;

        if (dQ[first] == i-k) {
            first ++;
        }


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


    }

    fileOut << suma;

    return 0;
}