#include <fstream>
using namespace std;
const int N=5000100;
int deque[N],x[N];
int main()
{
    ifstream f("deque.in");
    int n,k;
    f>>n>>k;
    for(int i=1;i<=n;++i)
        f>>x[i];
    long long sum=0;
    int front=1,back=0;
    for(int i=1;i<=n;++i)
    {
        while(back>=front&&x[i]<=x[deque[back]]) --back;
        deque[++back]=i;
        if(deque[front]==i-k)   ++front;
        if(i>=k) sum+=x[deque[front]];
    }
    f.close();
    ofstream h("deque.out");
    h<<sum<<'\n';
    h.close();
    return 0;
}