#include <bits/stdc++.h>
using namespace std;
ifstream f("deque.in");
ofstream g("deque.out");
int n,k,v[5000005];
int main()
{
    f>>n>>k;
    long long s=0;
    deque <int> dq;
    for(int i=1;i<=n;i++){
        f>>v[i];
        if(dq.front()==i-k)dq.pop_front();
        while(!dq.empty()&&v[dq.back()]>=v[i])dq.pop_back();
        dq.push_back(i);
        if(i>=k)s+=v[dq.front()];
    }
    g<<s;
    return 0;
}