#include <bits/stdc++.h>
#define N 5000005
using namespace std;
ifstream fin("deque.in");
ofstream fout("deque.out");
int n,k,i,j,Q[N],a[N],L,R;
long long s;
void rezolva()
{
    fin>>n>>k;
    for(i=1; i<=n; ++i)
    {
        fin>>a[i];
        while(L<=R&&a[Q[R]]>=a[i])
            R--;
        Q[++R]=i;
        if(i-Q[L]==k)
            ++L;
        if(i>=k)
            s+=a[Q[L]];
    }
    fout<<s;
}
int main()
{

    rezolva();

    return 0;
}