#include<cstdio>
#include<deque>
using namespace std;
int n,k,i;
unsigned long long s;
int v[5000001];
deque<int> dq;
int main()
{
    freopen("deque.in","r",stdin);
    freopen("deque.out","w",stdout);
    scanf("%d%d",&n,&k);
    for(i=1;i<=n;i++) scanf("%d",&v[i]);
    for(i=1;i<=k;i++)
    {
        while(!dq.empty()&&v[i]<=v[dq.back()])
            {
            dq.pop_back();
            }
            dq.push_back(i);

    }
    s=s+v[dq.front()];
    for(i=k+1;i<=n;i++)
    {
        if(dq.front()==i-k) dq.pop_front();
        while(!dq.empty()&&v[i]<=v[dq.back()])
            {
            dq.pop_back();
            }
        dq.push_back(i);
        s=s+v[dq.front()];
    }
    printf("%llu",s);
    return 0;
}