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

class min_deque{
    deque<int> dq;
public:
    min_deque(){}
    void push(const int n){
        while(!dq.empty() && dq.back() > n){
            dq.pop_back();
        }
        dq.push_back(n);
    }
    void pop(const int n){
        if(!dq.empty() && dq.front() == n){
            dq.pop_front();
        }
    }
    int front(){
        return dq.front();
    }
};

int main()
{
    ifstream f("deque.in");
    ofstream g("deque.out");
    int n, k;
    f >> n >> k;

    deque<int> dq;
    min_deque min_dq;

    for(int i = 0, x; i < k; ++i){
        f >> x;
        dq.push_back(x);
        min_dq.push(x);
    }

    long long rez = min_dq.front();
    for(int i = k, x; i < n; ++i){
        f >> x;

        min_dq.push(x);
        dq.push_back(x);
        min_dq.pop(dq.front());
        dq.pop_front();

        rez += (long long)min_dq.front();
    }
    g << rez << endl;
    return 0;
}