#include <fstream>
using namespace std;

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

int v[5000001], d[5000001];

int main()
{
    int st=0, dr=-1, n, k;
    long long sum=0;
    in >> n >> k;
    for(int 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;
}