#include <fstream>

using namespace std;
const int N = 5000001;
int d[N],v[N];
int main()
{
    ifstream in("deque.in");
    ofstream out("deque.out");
    int i,n,k,st,dr;
    long long sum = 0;
    in >> n >> k;
    st = 0;
    dr =-1;
    for(i=0;i<n;i++){
        in >> v[i];
        if(st <= dr && d[st] == i-k){
            st++;
        }
        while(st<=dr && v[i] <=v[d[dr]]){
            dr--;
        }
        d[++dr]=i;
        if(i>=k-1){
            sum +=v[d[st]];
        }
    }
    out << sum;

    return 0;
}