private static void Main()
{
int operationCount = FastIO.ReadNonNegativeInt();
var operations = new Operation[operationCount];
var possibleValues = new HashSet <int>();
for (int o = 0; o < operationCount; ++o)
{
operations[o] = new Operation(
operationType: FastIO.ReadOperationType(),
operationParameter: FastIO.ReadInt());
if (operations[o].OperationType == 'I')
{
possibleValues.Add(operations[o].OperationParameter);
}
}
var solver = new ORDERSET(possibleValues);
var output = new StringBuilder();
for (int o = 0; o < operationCount; ++o)
{
switch (operations[o].OperationType)
{
case 'I':
solver.Insert(value: operations[o].OperationParameter);
break;
case 'D':
solver.Delete(value: operations[o].OperationParameter);
break;
case 'K':
output.AppendLine(solver
.GetKthSmallest(k: operations[o].OperationParameter)
?.ToString() ?? "invalid");
break;
case 'C':
output.AppendLine(solver
.CountValuesSmallerThan(value: operations[o].OperationParameter)
.ToString());
break;
default: throw new InvalidOperationException();
}
}
Console.Write(output);
}