#include<fstream>
#include<deque>
#define maxn 5000005
using namespace std;
ifstream fi("deque.in");
ofstream fo("deque.out");

deque <int> deq;

int a[maxn],i,n,k;
long long s=0;

int main(){
    fi>>n>>k;
    
    for(i=1;i<=n;i++)
      {
       fi>>a[i]; 
       
       while(deq.size() && a[deq.back()]>=a[i]) deq.pop_back();
       
       deq.push_back(i);
       
       if(i>=k) s+=a[deq.front()];
       
       if(deq.front()==i-k+1) deq.pop_front();
      }
    
    fo<<s;
    
    fi.close();
    fo.close();
    return 0;
}