import java.util.*;

class Main{
    public static void main(String[] args){
        Scanner sc=new Scanner(System.in);
        int N=sc.nextInt();
        int K=sc.nextInt();
        
        long ans=0;
        
        for(int i=0;i<N;i++){
            long tmp=sc.nextLong();
            if(i<K-1){
                if(tmp<=1){
                    ans=tmp;
                }else{
                    ans+=tmp;
                }
            }else if(i==K-1){
                if(tmp==0){
                    System.out.println(0);
                    return;
                }else{
                    ans+=tmp;
                }
            }else{
                if(tmp<=1){
                    ans+=tmp;
                    System.out.println(ans);
                    return;
                }else{
                    ans+=tmp;
                }
            }
        }
        
        System.out.println(ans);
    }
}