#include<fstream>
#include<deque>
using namespace std;
ifstream cin("deque.in");
ofstream cout("deque.out");
deque<int> d;
int a[5000001];
int main()
{
    long long s=0;
    int k,n;
    cin>>n>>k;
    for(int i=1;i<=n;++i) {
        for(cin>>a[i];!d.empty()&&a[i]<=a[d.back()];d.pop_back());
        if(d.push_back(i),i-k>=d.front())
            d.pop_front();
        if(i>=k)
            s+=a[d.front()];
    }
    return cout<<s,0;
}