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#include <iostream>
int a(int n){int k=2,s=0;while(++k<n)s+=a(k)*a(n+~k);return s?s:1;}
int main()
{
int number;
std::cout << "n: ";
std::cin >> number;
std::cout << "nth number in Catalan sequence:"<<a(number)<<'\n';
}