Can u please explain the output of this program?

#1

#include <bits/stdc++.h>
using namespace std;
int main()
{
sets;
pair<set::iterator, bool> ret;
s.insert(1);
s.insert(5);
s.insert(10);
s.insert(3);
ret = s.insert(10);
cout<<ret.second<<endl;
return 0;
}

#2

The single element versions (1) return a pair, with its member pair::first set to an iterator pointing to either the newly inserted element or to the equivalent element already in the set. The pair::second element in the pair is set to true if a new element was inserted or false if an equivalent element already existed.

So since 10 is already present in the set
false === 0 is returned
hence the o/p is 0