#include <fstream>
#include <queue>

using namespace std;

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

deque<int> Q;
int n, k;
long long int v[5000005], suma;

int main() {
    fin >> n >> k;
    for(int i = 1; i <= n; i++) {
    	fin >> v[i];
    }
    for(int i = 1; i <= k; i++) {
        while(!Q.empty() && v[i] <= v[Q.back()]) {
        	Q.pop_back();
        }
    	Q.push_back(i);
    }
    for(int i = k + 1; i <= n; i++) {
        suma += v[Q.front()];
        while(!Q.empty() && Q.front() <= i - k) {
        	Q.pop_front();
        }
        while(!Q.empty() && v[i] <= v[Q.back()]) {
        	Q.pop_back();
        }
    	Q.push_back(i);
    }
    suma += v[Q.front()];
    fout << suma;
	return 0;
}