char a[1d3][1d3];
char by[1d3],bx[1d3];
{
	ll@n;
	rep(y,n){
		ll b=0;
		rep(x,n){
			char@s;
			b^=s&1;
			ll c=b;
			if(y) c^=a[y-1][x];
			a[y][x]=c;
			by[y]^=c;
			bx[x]^=c;
		}
		if(b){
			wt(-1);
			exit(0);
		}
	}
	rep(x,n){
		if(a[n-1][x]){
			wt(-1);
			exit(0);
		}
	}
	if(!(n&1)){
		rep(y,n-1){
			if(by[y]!=by[0]){
				wt(-1);
				exit(0);
			}
		}
		rep(x,n-1){
			if(bx[x]!=by[0]){
				wt(-1);
				exit(0);
			}
		}
	}
	ll z=0;
	rep(y,n-1){
		rep(x,n-1){
			z+=a[y][x]^=by[y]^bx[x];
		}
	}
	wt(z);
	rep(y,n-1){
		rep(x,n-1){
			if(a[y][x]){
				wt(y+1,x+1);
			}
		}
	}
}