int main(){int n,x,y,i,a[100];scanf("%d",&n);memset(a,0,400);void p(int c, int d){
printf("%d %d\n",c,d);}while(1){scanf("%d%d",&x,&y);if(x==-1)break;if(n-1!=y
&&a[i=(x+1)/2]<y)a[i]=y;}for(p(0,0),x=1;x<n-1;x++){for(y=0;y<=a[(x+1)/2];
y++)p(x,y);for(x++;0<=--y;)p(x,y);}for(y=0;y<n;y++)p(n,y);for(x=n;0<x;x--)
p(x,n);for(y=n;0<=y;y--)p(0,y);p(-1,-1);return 0;}//This is too low quality