#include <fstream>

using namespace std;

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

int n, k, v[5000005], d[5000005], u, p;
long long sum, val;

int main()
{
    fin>>n>>k;
    u = p =d[1] = 1;
    for(int i = 1; i <= n; i++){
        fin>>v[i];
    }
    for(int i = 2; i <= n; i++){
        while(v[i] < v[d[u]] && p <= u){
            --u;
        }
        d[++u] = i;
        if(i - d[p] == k){
            p++;
        }
        if(i >= k){
            sum += v[d[p]];
        }
    }
    fout<<sum;
    return 0;
}