View Compilation Error

0_0_34012996_26498.cpp: In function 'int main()':
0_0_34012996_26498.cpp:30:20: error: call of overloaded 'sqrt(ll&)' is ambiguous
         ll b=sqrt(a);
                    ^
0_0_34012996_26498.cpp:30:20: note: candidates are:
In file included from GCC4.9.2/x86_64-w64-mingw32/include/c++/cmath:44:0,
                 from GCC4.9.2/x86_64-w64-mingw32/include/c++/x86_64-w64-mingw32/bits/stdc++.h:41,
                 from 0_0_34012996_26498.cpp:1:
GCC4.9.2/x86_64-w64-mingw32/include/math.h:152:18: note: double sqrt(double)
   double __cdecl sqrt(double _X);
                  ^
In file included from GCC4.9.2/x86_64-w64-mingw32/include/c++/x86_64-w64-mingw32/bits/stdc++.h:41:0,
                 from 0_0_34012996_26498.cpp:1:
GCC4.9.2/x86_64-w64-mingw32/include/c++/cmath:486:3: note: constexpr long double std::sqrt(long double)
   sqrt(long double __x)
   ^
GCC4.9.2/x86_64-w64-mingw32/include/c++/cmath:482:3: note: constexpr float std::sqrt(float)
   sqrt(float __x)
   ^