#include <fstream>
#include <deque>

using namespace std;

deque<int> dq;
//int dq[5000000];
int v[5000000];

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

int main()
{
    int st = 0, dr = -1;
    int n;
    int k;
    long long s = 0;
    in >> n >> k;
    for(int i = 0; i < n; i++) {
        in >> v[i];
    }

    for(int i = 0; i < n; i++) {
        if(!dq.empty() && dq.front() == i-k) {
            dq.pop_front();
        }
        while(!dq.empty() && v[i] <= v[dq.back()]) {
            dq.pop_back();
        }
        dq.push_back(i);
        if(i >= k-1) {
            s += v[dq.front()];
        }
    }
    /*
    for(int i = 0; i < n; i++) {
        if(st <= dr && dq[st] == i-k) {
            st++;
        }
        while(st <= dr && v[i] <= v[dq[dr]]) {
            dr--;
        }
        dq[++dr] = i;
        if(i >= k-1) {
            s += v[dq[st]];
        }
    }
    */
    out << s;
}