/in/foo.cc:9:32: error: 'int y1' redeclared as different kind of symbol
 int f[maxn][maxn][3],n,m,x1,x2,y1,y2;
                                ^~
In file included from /usr/include/features.h:364:0,
                 from /usr/include/x86_64-linux-gnu/c++/6/bits/os_defines.h:39,
                 from /usr/include/x86_64-linux-gnu/c++/6/bits/c++config.h:507,
                 from /usr/include/c++/6/iostream:38,
                 from /in/foo.cc:1:
/usr/include/x86_64-linux-gnu/bits/mathcalls.h:251:1: note: previous declaration 'double y1(double)'
 __MATHCALL (y1,, (_Mdouble_));
 ^
/in/foo.cc: In function 'int main()':
/in/foo.cc:19:35: error: assignment of function 'double y1(double)'
       y1=min(a[h][k],a[h][(k+1)%3]);
                                   ^
/in/foo.cc:19:35: error: cannot convert 'const int' to 'double(double) throw ()' in assignment
/in/foo.cc:22:20: error: ISO C++ forbids comparison between pointer and integer [-fpermissive]
       if(x1>x2&&y1>y2)
                    ^~