#include <fstream>

using namespace std;
ifstream cin("deque.in");
ofstream cout("deque.out");
int v[5000001], c[5000001];
int main()
{
    int i, n, k, sf=0, in=0;
    long long  s=0;
    v[0]=-10000001;
    cin>>n>>k;
    for(i=1;i<=n;i++)
    {
        cin>>v[i];
        if(i<k)
        {
            while(in<=sf&&v[i]<v[c[sf]])
                sf--;
            sf++;
            c[sf]=i;
        }
        else
        {
            if(i-k+1>c[in])
                in++;
            while(in<=sf&&v[i]<v[c[sf]])
                sf--;
            sf++;
            c[sf]=i;
            s+=v[c[in]];
        }
    }
    cout<<s;
    return 0;
}