#include <iostream>
#include <fstream>
#include <algorithm>
#include <vector>
#include <bitset>
#include <stack>
#include <deque>
using namespace std;
ifstream in("deque.in");
ofstream out("deque.out");
long long n,x,v[5000001],sum,k;
deque <int> min_dq;
int main()
{
    int i;
    in>>n>>k;
    for(i=1;i<=n;i++)
        in>>v[i];
    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;
}