#include <fstream>
#include <deque>
using namespace std;
#define MAX 5000001
deque <int> deq;
int n, k, v[MAX];
ifstream fin("deque.in");
ofstream fout("deque.out");
int main()
{
    int i, x;
    long long rez=0;
    fin>>n>>k;
    for(i=1; i<=n; i++)
        fin>>v[i];
    for(i=1; i<=n; i++){
        while(!deq.empty() and v[i]<=v[deq.back()])
            deq.pop_back();
        if(!deq.empty() and i-k==deq.front())
            deq.pop_front();
        deq.push_back(i);
        if(i>=k)
            rez = rez + v[deq.front()];
    }
    fout<<rez;
    return 0;
}