#include <bits/stdc++.h>
using namespace std;
ifstream fin("deque.in");
ofstream fout("deque.out");
struct ceva
{
    int poz,val;
};
ceva a;
deque<ceva>dq;
int i,k,n,x;
long long s;
int main()
{
    fin>>n>>k;
    for(i=1;i<=n;i++)
    {
        fin>>x;
        while(!dq.empty() && dq.front().poz<i-k+1)
            dq.pop_front();
        while(!dq.empty() && dq.back().val>x)
            dq.pop_back();
        a.val=x;
        a.poz=i;
        dq.push_back(a);
        if(i>=k)
            s+=dq.front().val;
    }
    fout<<s;
    return 0;
}