import java.util.Stack;

public class NthMinFromBinaryTree {

	public static void main(String[] args) {
		TreeNode root = new TreeNode(12);
		root.left = new TreeNode(8);
		root.left.left = new TreeNode(7);
		root.left.right = new TreeNode(10);
		root.left.right.left = new TreeNode(9);
		root.right = new TreeNode(20);
		root.right.left = new TreeNode(14);
		root.right.left.right = new TreeNode(15);
		root.right.right = new TreeNode(21);
		System.out.println(getNthMin(root, 1));
	}
	
	public static int getNthMin(TreeNode root, int n) {
		Stack<TreeNode> st = new Stack<>();
		TreeNode current = root;
		while(current != null) {
			st.push(current);
			current = current.left;
		}
		while(!st.isEmpty() && n > 0) {
			current = st.pop();
			n--;
			if (current.right != null) {
				TreeNode subCurrent = current.right;
				while(subCurrent != null) {
					st.push(subCurrent);
					subCurrent = subCurrent.left;
				}
			}
		}
		return current.value;
	}
}