View Compilation Error

0_0_38504720_5098.cpp: In function 'void solve()':
0_0_38504720_5098.cpp:44:3: error: 'st' was not declared in this scope
   st.insert(a[i]);
   ^
0_0_38504720_5098.cpp:49:3: error: 'st' was not declared in this scope
   st.insert(c[i]);
   ^
0_0_38504720_5098.cpp:56:11: error: 'st' was not declared in this scope
  if ((int)st.size() != 6) {
           ^