View Compilation Error

0_0_38506029_20286.cpp: In function 'void S(ll, ll)':
0_0_38506029_20286.cpp:51:22: error: 'class std::unordered_set<long long int>' has no member named 'contains'
                 if(C.contains(k*q[z*a[x]%mod]%mod))ans=MIN(ans,make_pair(d[z],c[k*q[z*a[x]%mod]%mod]));
                      ^