#include <bits/stdc++.h>
using namespace std;
ifstream in ("date.in");
ofstream out ("date.out");

int n,k,v[5000005];
deque <int> min_dq;

int main()
{
    int i,x;
    in>>n>>k;
    for(i=1;i<=n;i++)
        in>>v[i];
    long long sum=0;
    for(i=1;i<=k;i++)
    {
        while(!min_dq.empty() and v[min_dq.back()]>v[i])
            min_dq.pop_back();
        min_dq.push_back(i);
    }
    sum+=v[min_dq.front()];
    for(i=k+1;i<=n;i++)
        {
            if(!min_dq.empty() and min_dq.front()<=i-k)
                min_dq.pop_front();
            while(!min_dq.empty() and v[min_dq.back()]>v[i])
                min_dq.pop_back();
            min_dq.push_back(i);
            sum+=v[min_dq.front()];
        }
    out<<sum;
    return 0;
}