#include <fstream>

using namespace std;
ifstream f("deque.in");
ofstream g("deque.out");
int i,n,v[5000001],dq[5000001],p,u,k;
long long S;
int main()
{   f>>n>>k;p=1;u=1;f>>v[1];
    dq[p]=1;
    for(i=2;i<=n;i++){
        f>>v[i];
        while(p<=u&&v[i]<=v[dq[u]])
            u--;
        dq[++u]=i;
        if(i-dq[p]>=k)
            p++;
        if(i>=k)
            S=S+v[dq[p]];
    }
    g<<S;
    return 0;
}