unordered_set_name.begin(n)

// CPP program to illustrate the
// unordered_set::begin() function
 
#include <iostream>
#include <unordered_set>
 
using namespace std;
 
int main()
{
 
    unordered_set<int> sampleSet;
 
    // Inserting elements in the std
    sampleSet.insert(5);
    sampleSet.insert(10);
    sampleSet.insert(15);
    sampleSet.insert(20);
    sampleSet.insert(25);
 
    auto itr1 = sampleSet.begin();
    auto itr2 = sampleSet.begin(4);
 
    cout << "First element in the container is: " << *itr1;
    cout << "\nFirst element in the bucket 4 is: " << *itr2;
 
    return 0;
}

First element in the container is: 25
First element in the bucket 4 is: 15