#include <fstream>
#include <cmath>
#include <algorithm>
#include <queue>
#include <deque>
#include <string>
#include <unordered_map>
#include <vector>
#include <stack>
#include <deque>
using namespace std;

ifstream cin("deque.in");
ofstream cout("deque.out");

deque<pair<int, int>> d;

int main(){
    long long n, k, summ=0;
    cin >> n >> k;
    int a;
    for(int i=1; i<=n; i++)
    {
        cin >> a;
        while(!d.empty() && a<d.back().first)
            d.pop_back();
        d.push_back({a, i});
        if(i>=k)
        {
            while(!d.empty() && d.front().second<=i-k)
                d.pop_front();
            summ+=d.front().first;
        }
    }
    cout << summ;
    
    
    return 0;
}