#include <iostream>
#include <fstream>
#define MAX 5000002
using namespace std;
int n,k,v[MAX],d[MAX],u,p;

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

int main()
{
    fin >> n >> k;
    for(int i = 1; i <= n; i++){
        fin >> v[i];
    }
    u = p = 1;
    d[1] = 1;
    long long ans = 0;
    for(int i = 1; i <= n; i++){
        while(p <= u && v[i] <= v[d[u]]){
            u--;
        }
        d[++u] = i;
        if(i-d[p] == k){
            p++;
        }
        if(i >= k){
            ans += v[d[p]];
        }
    }
    fout << ans << "\n";
    return 0;
}