#include<fstream>

using namespace std;

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

const int N = 5000000;

int v[N],dq[N];

int main()
{
    int st=0,dr=-1,i,n,k;
    long long s=0;
    fin>>n>>k;
    for(i=0;i<n;i++)
    {
        fin >> 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]];
    }
    fout<<s;
    return 0;
}