#include <fstream>

using namespace std;

ifstream cin("deque.in");
ofstream cout("deque.out");

int cod[5000005],v[5000005];

int main()
{
    int n,i,k,inc=1,sf=0;
    long long s=0;
    cin>>n>>k;
    for(i=1;i<=n;i++)
    {
        cin>>v[i];
        while(inc<=sf and v[i]<v[cod[sf]])
            sf--;
        cod[++sf]=i;
        if(cod[inc]==i-k)
            inc++;
        if(i>=k)
            s+=v[cod[inc]];
    }
    cout<<s;
    return 0;
}