#include <fstream>
using namespace std;

ifstream fin("deque.in");
ofstream fout("deque.out");
long long s;
int n, k, i, u, p, v[5000005], d[5000005];

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