#include<bits/stdc++.h>
#define ll long long
using namespace std;
ifstream in("deque.in");
ofstream out("deque.out");
int n,k,a[5000001];
ll s;
deque<int> q;
int main()
{in>>n>>k;
for(int i=1;i<=n;i++) {
    in>>a[i];
    if(!q.empty() && q.front()==i-k) q.pop_front();
    while(!q.empty() && a[i]<=a[q.back()])
        q.pop_back();
    q.push_back(i);
    if(i>=k) s+=a[q.front()];
    }
out<<s;
return 0;
}