View Compilation Error

0_0_13776445_12319.cpp: In function 'int main()':
0_0_13776445_12319.cpp:26:37: error: reference to 'minus' is ambiguous
   for( int i=1 ; i<x ; i++ ) tot += minus(a[i]-a[i-1],z);
                                     ^
0_0_13776445_12319.cpp:6:5: note: candidates are: int minus(int, int)
 int minus( int x, int y ){
     ^
In file included from GCC4.9.2/x86_64-w64-mingw32/include/c++/string:48:0,
                 from GCC4.9.2/x86_64-w64-mingw32/include/c++/bits/locale_classes.h:40,
                 from GCC4.9.2/x86_64-w64-mingw32/include/c++/bits/ios_base.h:41,
                 from GCC4.9.2/x86_64-w64-mingw32/include/c++/ios:42,
                 from GCC4.9.2/x86_64-w64-mingw32/include/c++/ostream:38,
                 from GCC4.9.2/x86_64-w64-mingw32/include/c++/iostream:39,
                 from 0_0_13776445_12319.cpp:1:
GCC4.9.2/x86_64-w64-mingw32/include/c++/bits/stl_function.h:176:12: note:                 template<class _Tp> struct std::minus
     struct minus : public binary_function<_Tp, _Tp, _Tp>
            ^