#include<fstream>
using namespace std;
ifstream in("deque.in");
ofstream out("deque.out");
int deq[5000002];
int v[5000002];
int main()
{
    int st=1,dr=0,n,k,i;
    long long s=0;
    in>>n>>k;
    for(i=1;i<=n;i++)
    {
        in>>v[i];
        while(st<=dr&&v[i]<=v[deq[dr]])
            dr--;
        deq[++dr]=i;
        if(deq[st]==i-k)
            st++;
        if(i>=k)
            s+=v[deq[st]];
    }
    out<<s;
    return 0;
}