#include <fstream>
#include <deque>
using namespace std;
ifstream cin("deque.in");
ofstream cout("deque.out");
deque<int> dq;
int v[5000000];
int main()
{
    int n,k;
    long long sum=0;
    cin>>n>>k;
    for(int i=0;i<n;i++){
        cin>>v[i];
    }
    for(int i=0;i<n;i++){
        if(!dq.empty()&&dq.front()<=i-k){
            dq.pop_front();
        }
        while(!dq.empty()&&v[dq.back()]>v[i]){
            dq.pop_back();
        }
        dq.push_back(i);
        if(i>=k-1){
            //cout<<dq.front()<<endl;
            sum+=v[dq.front()];
        }
    }
    cout<<sum;
}