#include <fstream>
#include <deque>
using namespace std;
ifstream f("deque.in");
ofstream g("deque.out");

#define NMAX 5000010
deque<int>C;
int a[NMAX];
int n, k;
long long S;

int main()
{
    int i;
    f>>n>>k;
    for(i = 1; i <= n; i++)
        f>>a[i];
    C.push_back(1);
    for(i = 2; i <= k; i++)
    {
        while(a[i] <= a[C.back()] && !C.empty())
            C.pop_back();
        C.push_back(i);
    }
    S += a[C.front()];
    for(i = k + 1; i <= n; i++) {
        if(i - k >= C.front() && !C.empty())
            C.pop_front();
        while(a[i] <= a[C.back()] && !C.empty())
            C.pop_back();
        C.push_back(i);
        S += a[C.front()];
    }
    g<<S<<'\n';
    return 0;
}