#include <fstream>
using namespace std;
ifstream in("deque.in");
ofstream out("deque.out");
int n, k;
int a[5000001], b[5000001];
int s, d;
long long r;
int main(){
    int i;
    in>>n>>k;
    for(i=1;i<=n;i++){
        in>>a[i];
    }
    s=1;d=0;
    for(i=1;i<=n;i++){
		while(s<=d && a[i]<=a[b[d]]){
            d--;
		}
		b[++d]=i;
		if(b[s]==i-k){
            s++;
		}
		if(i>=k){
            r+=a[b[s]];
		}
	}
    out<<r;
    return 0;
}