#include <fstream>
#include <deque>
using namespace std;


ifstream fin("deque.in");
ofstream fout("deque.out");


struct element{
    int val, pos;
};

deque<pair<int, int>> v;

int main(){
    int n, k;

    fin>>n>>k;
    long long s = 0;

    for (int i = 1; i<=n; i++){
        int x;
        fin>>x;

        while (!v.empty()&& v.back().first>x){
            v.pop_back();
        }

        v.push_back({x, i});

        while(v.front().second<i-k+1)
            v.pop_front();

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

    fout<<s;
}