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