View Compilation Error

0_0_29805493_11047.cpp: In function 'void calc()':
0_0_29805493_11047.cpp:59:61: error: 'a' was not declared in this scope
         F[0][i]=1ll*fact[cnt[i]]*fact[n-cnt[i]+1]%mod*C(n+1,a-cnt[i]+2);
                                                             ^