#include <iostream>
#include <fstream>
using namespace std;
int coada_dubla[5000005];
int st = 0;
int dr = -1;
long long sum =  0;

int main() {

    ifstream f ("deque.in");
    ofstream g ("deque.out");
    int n, k, v[5000005];
    f >> n >> k;
    for (int i = 0; i < n; i++)
        f >> v[i];


    for (int i = 0; i < n; ++i) {
        while(st <= dr && v[i] < v[coada_dubla[dr]])
            dr--;
        dr++;
        coada_dubla[dr] = i;
        if (coada_dubla[st] == i-k) 
            st++;
        if (i >= k-1)
            sum += v[coada_dubla[st]];
    }
    g << sum;
    return 0;
}