#include <fstream>

using namespace std;
ifstream cin("deque.in");
ofstream cout("deque.out");
int n,k,v[5000005],dq[5000005],st,dr;
long long s;
int main()
{
    cin>>n>>k;
    for(int i=1; i<=n; i++)
        cin>>v[i];
    dq[1]=1;
    st=1;
    dr=1;
    for(int i=2; i<=n; i++)
    {
        while(st<=dr&&v[i]<v[dq[dr]])
            dr--;
        dq[++dr]=i;
        if(dq[st]==i-k)
            st++;
        if(i>=k)
        s+=v[dq[st]];

    }
    cout<<s;
    return 0;
}