#include <cstdio>
#include <deque>
using namespace std;
deque<int>d;
deque<int>poz;
int main() 
{
    freopen("deque.in", "r", stdin);
    freopen("deque.out", "w", stdout);
    int n, k, i, nr;
    long long sum = 0;
    scanf("%d%d", &n, &k);
    for(i = 1; i <= n; i++) 
    {
        scanf("%d", &nr);
        while(!d.empty()) 
        {
            if(d.back() > nr)d.pop_back(), poz.pop_back();
            else break;
        }
        d.push_back(nr);
        poz.push_back(i);
        if(i >= k)sum += d.front();
        if(poz.front() == (i - k + 1) && i >= k)
            d.pop_front(), poz.pop_front();
    }
    printf("%lld", sum);
    return 0;
}