#include <fstream>

using namespace std;

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

const int N =50000;

int v[N],dq[N];

int main()
{
    int st=0,dr=-1,i,n,k;
    long long s=0;
    in>>n>>k;
    for(i=0; i<n; i++)
    {
        in>>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=s+v[dq[st]];


    }
    out<<s;
    return 0;
}