#include <fstream>
#include <deque>

using namespace std;

ifstream f("deque.in");
ofstream g("deque.out");

int main()
{
    unsigned long long n,k,s=0;
    deque<unsigned long long> dq,dp;

    f>>n>>k;

    for(int i=1;i<=n;i++){
        unsigned long long x;
        f>>x;

        while(!dp.empty()&&dp.front()<=i-k){
            dp.pop_front();
            dq.pop_front();
        }

        while(!dq.empty()&&x<=dq.back()){
            dq.pop_back();
            dp.pop_back();
        }
        dq.push_back(x);
        dp.push_back(i);

        if(i>=k)
            s+=dq.front();
    }

    g<<s;

    return 0;
}