#include <fstream>

using namespace std;

ifstream cin("deque.in");
ofstream cout("deque.out");

const int N=5000005;
int v[N],dq[N];

int main()
{
    int n,k,i,st=0,dr=-1;
    long long s=0;
    cin>>n>>k;
    for(i=0; i<n; i++)
    {
        cin>>v[i];
        if (st<=dr&&dq[st]==i-k)
        {
            st++;
        }
        while (st<=dr&&v[i]<=v[dq[dr]])
        {
            dr--;
        }
        dq[++dr]=i;
        if (i>=k-1)
        {
            s+=v[dq[st]];
        }
    }
    cout<<s;
    return 0;
}