View Compilation Error

0_0_10235930_8142.cpp: In function `void Topologicsort()':
0_0_10235930_8142.cpp:35: error: no matching function for call to `std::set<int, std::less<int>, std::allocator<int> >::insert()'
GCC/bin/../lib/gcc/mingw32/3.4.2/../../../../include/c++/3.4.2/bits/stl_set.h:313: note: candidates are: std::pair<typename std::_Rb_tree<_Key, _Key, std::_Identity<_Key>, _Compare, _Alloc>::const_iterator, bool> std::set<_Key, _Compare, _Alloc>::insert(const _Key&) [with _Key = int, _Compare = std::less<int>, _Alloc = std::allocator<int>]
GCC/bin/../lib/gcc/mingw32/3.4.2/../../../../include/c++/3.4.2/bits/stl_set.h:339: note:                 typename std::_Rb_tree<_Key, _Key, std::_Identity<_Key>, _Compare, _Alloc>::const_iterator std::set<_Key, _Compare, _Alloc>::insert(typename std::_Rb_tree<_Key, _Key, std::_Identity<_Key>, _Compare, _Alloc>::const_iterator, const _Key&) [with _Key = int, _Compare = std::less<int>, _Alloc = std::allocator<int>]