View Compilation Error

0_0_38404872_24040.cpp:4:11: error: conflicting declaration 'int c'
 int a, b, c, d, ht[mxn<<1], ans;
           ^
0_0_38404872_24040.cpp:3:24: note: previous declaration as 'const int c'
 const int mxn = 1e6+5, c = 1e6;
                        ^