#include <bits/stdc++.h>

using namespace std;

ifstream f("deque.in");
ofstream g("deque.out");

int n,k,v[5000005];
long long sum=0;
deque<int> coada;

int main()
{
 f>>n>>k;
 for(int i=1;i<=n;i++) f>>v[i];

 for(int i=1;i<=n;i++)
 {
   while( !coada.empty()&&i-k+1>coada.front() ) coada.pop_front();
   while( !coada.empty()&&v[i]<=v[coada.back()] ) coada.pop_back();
   coada.push_back(i);
   if(i>=k) sum+=v[coada.front()];
 }
 g<<sum;
}