#include <bits/stdc++.h>
using namespace std;
ifstream fin("deque.in");
ofstream fout("deque.out");
deque<pair<long long,int>>Q;
int main()
{
    int n,i,k;
    long long s=0,x;
    fin>>n>>k;
    for(i=1; i<=n; i++)
    {
        fin>>x;
        while(Q.empty()==0 && Q.back().first>x)Q.pop_back();
        Q.push_back(make_pair(x,i));
        if(Q.front().second<i-k+1)Q.pop_front();
        if(i>=k)s+=Q.front().first;
    }
    fout<<s;
}