#include <fstream>

using namespace std;

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

const int N=5000001;
int v[N],dq[N];

int main()
{
    int n,k,i,st,dr;
    long long s;
    cin>>n>>k;
    s=0;
    st=0;
    dr=-1;
    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;
}