#include <fstream>

using namespace std;
ifstream cin("deque.in");
ofstream cout("deque.out");
long long v[5000000],dq[500000];
int main()
{
    long long n,k,s=0;
    cin>>n>>k;
    int st=0,dr=-1;
    for(int i=0;i<n; i++)
    {
        cin>>v[i];
        if(i>=k&&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;
}