#include <bits/stdc++.h>
#define valoare first
#define pozitie second
#define perechea make_pair

using namespace std;
ifstream f("deque.in");
ofstream g("deque.out");
int n,k,x;
int64_t s;
list<pair<int,int>> Q;
int main()
{
    f>>n>>k;
    for(int i=1;i<k;i++)
    {
        f>>x;
        while(Q.size()&&x<=Q.back().valoare)
            Q.pop_back();
        Q.push_back(perechea(x,i));
    }
    for(int i=k;i<=n;i++)
    {
        f>>x;
        while(Q.size()&&x<=Q.back().valoare)
            Q.pop_back();
        Q.push_back(perechea(x,i));
        if(i-Q.front().pozitie==k)
            Q.pop_front();
        s+=Q.front().valoare;
    }
    g<<s;
    return 0;
}