#include <bits/stdc++.h>

using namespace std;
ifstream in("deque.in");
ofstream out("deque.out");
deque<pair<long long,int>> q;
long long n,k,x,y,s;
int main()
{
    in>>n>>k;
    for(int i=1;i<=n;i++)
    {
        in>>x;
        if(!q.empty()&&q.front().second<i-k+1) q.pop_front();
        while(!q.empty()&&x<=q.back().first) q.pop_back();
        q.push_back({x,i});
        if(i>=k) s+=q.front().first;
    }
    out<<s;
    return 0;
}