#include <fstream>
#include <iostream>
#define dim 5000010

std::ifstream fin("deque.in");
std::ofstream fout("deque.out");

int v[dim], dek[dim];

int main() {
    long long sum = 0;
    int n, k, nr;

    int front = 1, back = 0;

    fin >> n >> k;
    
    for(int i = 1; i <= n; i++) {
        fin >> v[i];
    }

    for(int i = 1; i <= n; i++) {
        while( front <= back && v[i] <= v[ dek[back] ] )
            back--;

        dek[++back] = i;  

        if(dek[front] == i - k)
            front++;

        if(i >= k)
            sum += v[ dek[front] ];
            // std::cout << v[ dek[front] ] << " ";
    }

    // std::cout << '\n' << sum << '\n';
    fout << sum;

    return 0;
}