Find element occuring n times

int duplicate(vector<int> &arr,int b){
    int n=arr.size();
    unordered_map<int,int> freq;
    for(int i=0;i<n;i++){
        freq[arr[i]]++;
    }
        for(auto c:freq )
        if(c.second==b){
            return c.first;
        }
    
   return -1;
   
}