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