#include <deque>
#include <cstdio>
using namespace std;
deque <int> T;
int n, x, k;
long long a[5000005];
long long s=0;
int main()
{
    freopen("deque.in", "r", stdin);
    freopen("deque.out","w",stdout);
    scanf("%d %d\n",&n, &k);
    for(int i=1; i<=n; i++){
        scanf("%lld\n",&a[i]);
        while(!T.empty() && a[T.back()]>=a[i])
            T.pop_back();
        T.push_back(i);
        while(!T.empty() && T.front()<i-k+1){
            T.pop_front();
        }
        if(T.front()>=k)
            s+=a[T.front()];
    }
    printf("%lld",s);
    return 0;
}