#include <cstdio>
#include <deque>

using namespace std;

deque <int> q;

int v[500005];

int main()
{
    freopen("deque.in","r",stdin);
    freopen("deque.out","w",stdout);

    int n,k,i;
    long long sum=0;

    scanf("%d%d",&n,&k);

    for(i=1;i<=n;i++)
    {
        scanf("%d",&v[i]);

        while(!q.empty())
        {
            if(v[q.back()]>=v[i]) q.pop_back();
            else break;
        }

        q.push_back(i);

        while(q.front()<i-k+1) q.pop_front();

        if(i>=k) sum+=v[q.front()];
    }

    printf("%lld\n",sum);

    return 0;
}