View Compilation Error

0_0_36603696_18479.cpp: In function 'int main()':
0_0_36603696_18479.cpp:39:7: error: cannot convert '__gnu_cxx::__normal_iterator<int*, std::vector<int> >' to 'int' in assignment
     id=it-1;//找到<=ins的最大数 (注意：-a.begin() ) 
       ^