# include <cstdio>
# include <deque>
# define pb push_back
# define popb pop_back
# define popf pop_front
# define MAXN 5000005

using namespace std;

int N,K,i;
long long S;
int a[MAXN];
deque <int> h;

int main()
{
    freopen("deque.in", "r", stdin);
    freopen("deque.out", "w", stdout);
    scanf("%d %d\n", &N, &K);
    for(i=1; i<=N; ++i)
    {
        scanf("%d\n", &a[i]);
        while(h.size() && a[h.back()]>=a[i]) h.popb();
        h.pb(i);
        if(i>=K) S+=a[h.front()];
        if(h.front()==i-K+1) h.popf();
    }
    printf("%lld\n", S);
    fclose(stdin);
    fclose(stdout);
    return 0;
}