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