#include <bits/stdc++.h>

using namespace std;
ifstream f("deque.in");
ofstream g("deque.out");
deque<pair<int,int>> Q;
int n,i,k,x;
long long s;

int main()
{
    f>>n>>k;
    for(i=1; i<k; i++)
    {
        f>>x;
        while(Q.size()&&Q.back().first >=x)
            Q.pop_back();
        Q.push_back(make_pair(x,i));
    }
    for(i=k;i<=n;i++)
    {
        f>>x;
        while(Q.size()&&Q.back().first >=x)
            Q.pop_back();
        Q.push_back(make_pair(x,i));
        if(Q.front().second==i-k)
            Q.pop_front();
        s+=Q.front().first;
    }
    g<<s;
    return 0;
}