/in/foo.cc: In function 'int main()':
/in/foo.cc:14:3: error: 'd' was not declared in this scope
   d=n*(n-1)*(2*n-1)/6%mod;
   ^
/in/foo.cc:6:27: warning: unused variable 'b' [-Wunused-variable]
  ll mod=(ll)1e9+7,t,n,m,a,b,c;
                           ^