#include <fstream>
#include <deque>
using namespace std;
ifstream fin("deque.in");
ofstream fout("deque.out");
deque <int> d;
int a[5000005],n,k,i;
long long sum;
int main()
{
    fin>>n>>k;
    for(i=1;i<k;i++)
    {
        fin>>a[i];
        while(!d.empty()&&a[d.back()]>a[i])
            d.pop_back();
        d.push_back(i);
    }
    for(i=k;i<=n;i++)
    {
        fin>>a[i];
        while(!d.empty()&&a[d.back()]>a[i])
            d.pop_back();
        d.push_back(i);
        if(i-d.front()+1>k)
            d.pop_front();
        sum+=a[d.front()];
    }
    fout<<sum;
    return 0;
}