#include<fstream>
using namespace std;
int n, i, p, u, k;
int v[500001], d[5000001];
long long sum;
ifstream fin("deque.in");
ofstream fout("deque.out");
int main(){
    fin>> n >> k;
    for(i = 1; i <= n; i++){
        fin>> v[i];
    }
    p = 1;
    u = 1;
    d[1] = 1;
    for(i = 2; i <= n; i++){
        while(p <= u && v[i] < v[d[u]]){
            u--;
        }
        u++;
        d[u] = i;
        if(i - d[p] == k){
            p++;
        }
        if(i >= k){
            sum += v[d[p]];
           // fout<< v[d[p]] <<" ";
        }
    }
    fout<< sum;
    return 0;
}