#include <iostream>
#include <fstream>

std::ifstream f("deque.in");
std::ofstream g("deque.out");

int deq[5000001], sir[5000001];
int main(){
    int n, k;
    f >> n >> k;

    int st = 0, dr = -1;
    long long suma = 0;
    
    for(int i = 0; i < n; i++)
        f >> sir[i];
    
    for(int i = 0; i < n; i++){
        while(st <= dr && sir[i] <= sir[deq[dr]])
            --dr;
        ++dr;
        deq[dr] = i;

        if(i - k == deq[st]) 
            ++st;
        
        if(i >= k - 1)
            suma += sir[deq[st]];
    }

    g << suma;
    f.close();
    g.close();
    return 0;
}