View Compilation Error

0_0_26419743_5956.cpp:6:5: error: conflicting declaration 'int N'
 int N,a,b;
     ^
0_0_26419743_5956.cpp:4:21: note: previous declaration as 'const long long int N'
 const long long int N = 2147493647;   
                     ^
0_0_26419743_5956.cpp: In function 'int main()':
0_0_26419743_5956.cpp:61:10: error: assignment of read-only variable 'N'
         N=N-2;
          ^
0_0_26419743_5956.cpp:66:11: error: assignment of read-only variable 'N'
          N=N/2;
           ^
0_0_26419743_5956.cpp:69:34: error: 'mod' was not declared in this scope
         sum=(sum+b*center[0][0])%mod;
                                  ^