C++ STL what will be the output and explain why will that be

[jekaks7288_f681389b2ca0b208]

#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;
}