#include <fstream>
#include <deque>
using namespace std;
ifstream cin("deque.in");
ofstream cout("deque.out");

deque<int> d;
int v[5000010];
int n,i,k;
__int64 sum;
int main()
{
    cin>>n>>k;
    for(i=1;i<=k;++i)
    {
        cin>>v[i];
        if(!d.empty())
            while(v[i]<v[d.back()])
            {
                d.pop_back();
                if(d.empty()) break;
            }
        d.push_back(i);
    }
    sum+=v[d.front()];
    for(i=k+1;i<=n;++i)
    {
        cin>>v[i];
        if(!d.empty() && d.front()<=i-k)
            d.pop_front();
        if(!d.empty())
            while(v[i]<v[d.back()])
            {
                d.pop_back();
                if(d.empty()) break;
            }
        sum+=v[d.front()];
        d.push_back(i);
    }
    cout<<sum;
    return 0;
}