#include <fstream>
using namespace std;
int n, k, D[5000004], v[5000004];
long long s;
int main(){
    ifstream fin ("deque.in");
    ofstream fout("deque.out");
    fin>>n>>k;
    for(int i=1;i<=n;i++){
        fin>>v[i];
    }
    int p=1, u=1;
    D[1]=1;
    for(int i=2;i<=n;i++){
        while(v[i]<v[D[u]] && p<=u){
            u--;
        }
        D[++u]=i;
        if(i-D[p]==k)
            p++;
        if(i>=k){
            //fout<<v[D[p]]<<"\n";
            s+=v[D[p]];
        }
    }
    fout<<s;



    return 0;
}