# include <fstream>
using namespace std;
ifstream fin("deque.in");
ofstream fout("deque.out");
int i,n,k,x,v[5000001],d[5000001],u,p;
long long s;
int main () {
    fin>>n>>k;
    u=0;
    p=1;
    for(i=1;i<=n;i++){
        fin>>v[i];
        while(p<=u&&v[i]<=v[d[u]])
            u--;
        u++;
        d[u]=i;
        if(i-d[p]==k)
            p++;
        if(i>=k)
            s=s+v[d[p]];
    }
    fout<<s;
    return 0;
}