#include <fstream>      
       
 using namespace std;    
 int v[5000010], st[5000010], p, u, n, k;      
 long long s;      
 int main()      
 {      
     ifstream f ("deque.in");      
     ofstream g ("deque.out");      
     int i;       
     f>>n>>k;    
     for(i=1;i<=n;i++)  f>>v[i];      
     p=1, u=0;    
     for(i=1;i<=n;i++)    
     {      
         while((p<=u)&&(v[i]<=v[st[u]])) u--;           
         st[++u]=i;      
         if(st[p]==i-k) p++;      
         if(i>=k) s+=v[st[p]];           
     }      
     g<<s;      
     return 0;      
}