import java.util.*; 
 public class work2 {
  public static void main(String[] args) {
    Scanner input=new Scanner(System.in); 	   
    System.out.print("input array size:");
    int size=input.nextInt();
    int [][] list = new int[size][size];
    int i,j;
    for(i=0;i<size;i++){
    	for(j=0;j<size;j++){
    		System.out.print("input array value for list["+(i+1)+"]["+(j+1)+"]:");
    		list[i][j]=input.nextInt();
    	}
    }
    int sum=0;
    for(i=0;i<size;i++){
    	sum=sum+list[i][i];
    }
	for(i=0,j=size-1;i<size;j--,i++){
		sum=sum+list[i][j];
	}
	System.out.print(sum);
  }
}