#include <fstream>
#include <cstring>
using namespace std;
ofstream fout("deque.out");
ifstream fin("deque.in");
const int NMAX = 5000005;

int n, k, Front = 1, Back;
int Deque[NMAX], v[NMAX];
long long suma;

int main()
{
    fin >> n >> k;
    for(int i=1; i<=n; i++) fin >> v[i];

    for(int i=1; i<=n; i++) {
        while(Front <= Back && v[i] <= v[Deque[Back]]) Back--;

        Deque[++Back] = i;

        if(Deque[Front] == i - k) Front++;

        if(i >= k) suma += v[Deque[Front]];
    }

    fout << suma << '\n';
    return 0;
}