View Compilation Error

In file included from GCC4.9.2/x86_64-w64-mingw32/include/c++/cassert:43:0,
                 from 0_0_15074844_24395.cpp:5:
0_0_15074844_24395.cpp: In function 'void solve()':
0_0_15074844_24395.cpp:68:9: error: 'ans' was not declared in this scope
  assert(ans >= 0);
         ^