View Compilation Error

0_0_33711016_8117.cpp: In function 'int main()':
0_0_33711016_8117.cpp:26:28: error: 'ans' was not declared in this scope
             if(i==1||i==n) ans+=a;
                            ^
0_0_33711016_8117.cpp:29:15: error: 'ans' was not declared in this scope
         cout<<ans * 250000002 % 1000000007;
               ^