#include <iostream>
#include <fstream>
#include <deque>
#include <algorithm>
using namespace std;
ifstream si("deque.in");
ofstream so("deque.out");
deque<int> v,p;

int main() {
    int n,k;
    si>>n>>k;
    for(int i=0; i<k; ++i) {
        int a;
        si>>a;
        while(v.size()>0&&v.back()>a) {
            v.pop_back();
            p.pop_back();
        }
        v.push_back(a);
        p.push_back(i);
    }
    long long s;
    s=1LL*v.front();
    for(int i=k; i<n; ++i) {
        int a;
        si>>a;
        while(v.size()>0&&v.back()>a)
        {
            v.pop_back();
            p.pop_back();
        }
        v.push_back(a);
        p.push_back(i);
        if(p.front()==i-k)
        {
            p.pop_front();
            v.pop_front();
        }
        s=s+1LL*v.front();
    }
    so<<s<<'\n';
    return 0;
}