#include <fstream>
#include <queue>

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

const int MAXN = 5000000;
int v[1 + MAXN];
std::deque <int> dq;

int main(){
    int n, k;
    in >> n >> k;
    for(int i = 1; i <= n; i++)
        in >> v[i];
    long long sum = 0LL;
    for(int i = 1; i <= n; i++){
        in >> v[i];
        while(!dq.empty() && v[dq.back()] >= v[i])
            dq.pop_back();
        dq.push_back(i);
        while(!dq.empty() && i - dq.front() + 1 > k)
            dq.pop_front();
        sum += v[dq.front()] * (i >= k);
    }
    out << sum;
    return 0;
}