#include <fstream>

using namespace std;

ifstream fin("deque.in");
ofstream fout("deque.out");

int v[5000010],D[5000010],i,u,p,n,k;
long long s;
int main()
{
    fin >> n >> k;
    p=1; u=0;
    for(i=1;i<=n;i++){
        fin >> v[i];
        while(p<=u && v[i]<v[D[u]])
            u--;
        D[++u]=i;
        if(i-D[p] == k)
            p++;
        if(i>=k)
        s+=v[D[p]];
    }
    fout << s;
    return 0;
}