#include <cstdio>
#include <deque>

using namespace std;

int v1[5000010];
deque<int> v;

int main()
{
    freopen("deque.in","r",stdin);
    freopen("deque.out","w",stdout);
    int n,k;
    long long s=0;
    scanf("%d%d",&n,&k);
    for(int i=1;i<=n;i++)
    {
        scanf("%d",&v1[i]);
        if(v.front()==i-k) v.pop_front();
        if(v.empty()) v.push_back(i);
        else
        while(!v.empty())
            if(v1[v.back()]>=v1[i]) v.pop_back();
            else {v.push_back(i);break;}
        if(v.empty()) v.push_back(i);
        if(i>=k) s=s+v1[v.front()];
    }
    printf("%lld",s);
    return 0;
}