* Definition for a binary tree node.
* TreeNode(int x) : val(x), left(NULL), right(NULL) {}
void traversal(TreeNode* root)
if(root->val < min_fir) {min_sec=min_fir; min_fir=root->val ; ++count;}
else if(root->val > min_fir && root->val <= min_sec) { min_sec=root->val; ++count;}
int findSecondMinimumValue(TreeNode* root) {
// cout<<min_fir<<" "<< min_sec<<endl;
return count<2 ? -1 : min_sec;