#include <fstream>

using namespace std;
ifstream fin("deque.in");
ofstream fout("deque.out");
int v[5000005], deque[5000005], n, k, st, dr;
long long Sol;
int main()
{
    fin>>n>>k;
    st=1, dr=0;
    for(int i=1;i<=n;i++)
    {
        fin>>v[i];
        while(v[i]<=v[deque[dr]] && st<=dr)
            dr--;
        deque[++dr]=i;
        if(deque[st]==i-k)
            st++;
        if(i>=k)
            Sol+=v[deque[st]];
    }
    fout<<Sol;
    return 0;
}