#include <fstream>

using namespace std;

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

int n, k, st, dr, v[5000100], Deque[5000100];
long long S;

int main()
{
    f >> n >> k;
    for(int i=1; i<=n; i++) f >> v[i];
    st = 1; dr = 0;
    for(int i=1; i<=n; i++)
    {
        while(st <= dr && v[i] <= v[Deque[dr]]) dr--;
        Deque[++dr] = i;
        if(Deque[st] == i-k) st++;
        if(i >= k) S+=v[Deque[st]];
    }
    g << S << '\n';
    return 0;
}