How to solve this Floating Point expection: 8 error

Question

This program is suppose to take a json in the format of a dict. The keys are zipcodes and the values are vectors of rent prices.

When i run it using g++ I get a floating point exception 8: error. To my knowledge that error only triggers if the value overflows its data type but that could only occur if the averager function's mean variable is surpassing the max value of an unsigned long long which shouldn't occur.

I am also open to a more elegant way to write this code.

#include <iostream>
#include <fstream>
#include <string>
#include <vector>
#include <nlohmann/json.hpp>

using json = nlohmann::json;
using namespace std;

unsigned int average(unsigned int n1,unsigned int n2){
    unsigned int mean;
    mean = (n1 + n2)/2;
    return mean;
}

unsigned long long average(vector<unsigned int> nValues){
    unsigned long long mean = 0;
    for(auto element : nValues){
        mean += element;
    }
    mean /= nValues.size();
    return mean;
}

unsigned int strCleaner(string str){
    unsigned int na = 0;
    string temp;
    if(str == "N/A"){
        return na;
    }
    for(auto element : str){
        if(element == '$' || element == ',' || element == ' ' || element == '"'){
            continue;
        }
       temp += element;
    }
    cout << temp << endl;
    int newStr = stoi(temp);
    return (unsigned int)newStr;
}

int main(void)
{
    string line;
    ifstream my_json("records_v1.json");
    ifstream zips("zip_set.txt");
    json my_stat;
    json j;
    my_json >> j;
    while(getline(zips,line)){
        vector<unsigned int> summation; 
        auto map = j[line];
        for(auto element: map){
            string element_str = element.dump();
            size_t result = element_str.find("-");
            if(result != string::npos){
                string n1, n2;
                for (int i = 0; i < element_str.size(); i++)
                {
                    if(i < result){
                        n1 += element_str[i];
                    }
                    if(i > result){
                        n2 += element_str[i];
                    }
                }
               auto mean = average(strCleaner(n1),strCleaner(n2));
               summation.push_back(mean);

            }else if(element_str != "N/A"){
                continue;
                
            }else{
                unsigned int cleanedInt = strCleaner(element);
                summation.push_back(cleanedInt);
            }
        }
        auto city_mean = average(summation);
        my_stat[line] = city_mean; 
    
    }
    ofstream f_myrecord("fileZ.json");
    f_myrecord << setw(4) << my_stat << endl;
}