Q. What is the output of this program?

#include
using namespace std;
int add(int p, int q);
int main()
{
int n = 15, m = 16;
cout << add(n, m) << endl;
return 0;
}
int add(int p, int q )
{
int sum = p + q;
p = 20;
return p + q;
}