/in/foo.cc: In function 'int main()':
/in/foo.cc:13:13: error: 'a' was not declared in this scope
             a[f[i]+f[j]]=0;
             ^
/in/foo.cc:17:12: error: 'a' was not declared in this scope
         if(a[f[i]]==0)ans++;
            ^