Why 0 is printing as most significant digit in c++

In the following program, I have attached code and its sample output I don't know why it is printing 0 as the most significant digit. I have tried different test cases but it just adds 0 to most significant digit.
Is it a bug or I'm missing some concept.

#include<bits/stdc++.h>
using namespace std;
int kthLargest (vector<int> arr, int n, int k){
  map<int,int> a;
  cout<<a.size();
  vector<int>::iterator i;
  for(i=arr.begin();i!=arr.end();i++)
  {
    a[*i]=a[*i]+1;
  }
  map<int,int>::iterator j;
  int sum=0;
  for(j=a.begin();j!=a.end();j++)
  {
    sum+=j->second;
    if(sum>(n-k))
    {
      sum=j->first;
      break;
    }
  }
  return sum;
}
int main()
{
    ios_base::sync_with_stdio(false);
    cin.tie(NULL);
    int n;
    cin>>n;
    vector<int> a(n);
    for (int i = 0; i < n; ++i)
    {
        cin>>a[i];
    }
    int k;
    cin>>k;
    cout<<kthLargest(a,n,k);
    return 0;
}

output

5
1 2 3 4 5
3

output

04