#include <fstream>

using namespace std;

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

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

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