View Compilation Error

0_0_25411563_19463.cpp: In function 'int main()':
0_0_25411563_19463.cpp:39:54: error: increment of read-only location 'it.std::_Rb_tree_const_iterator<_Tp>::operator*<e>().e::g[1][1]'
             else if((*it).f[1][1] == w) (*it).g[1][1]++, (*G[v].find(e(0, u))).g[1][1]++;
                                                      ^
0_0_25411563_19463.cpp:39:87: error: increment of read-only location 'G[v].std::set<_Key, _Compare, _Alloc>::find<e, std::less<e>, std::allocator<e> >((*(const key_type*)(& e(0, u, -1)))).std::_Rb_tree_const_iterator<_Tp>::operator*<e>().e::g[1][1]'
             else if((*it).f[1][1] == w) (*it).g[1][1]++, (*G[v].find(e(0, u))).g[1][1]++;
                                                                                       ^