include

Use long long instead of just long

#include<bits/stdc++.h>
using namespace std;
int main() { int n = 0; std::cin >> n;

for (int i = 0; i < n; i++)
{
    long long  total = 0;
    long long  a = 0;
    long long b = 0;
    long long c = 0;
    std::cin >> a;
    std::cin >> b;
    std::cin >> c;
    total = a+b+c;
    if ((long long)(total)%2==0)
        std::cout<<total/2 <<"\n";
    else
        std::cout<<(total-1)/2 <<"\n";

}
return 0;
}

Try long long instead of long. You can read more here. Also please add submission link instead of copy/pasting in the blog, or use the block format for your code:

#include <bits/stdc++.h>

Using ``` before and after it (With enter).

This is because you are converting long to int. You shouldn't do that since the constraints are pretty big (10^16 — whereas max int can go is something of order 10^9) and then the long value will give just some garbage value. Also, you don't need to do that since modulo will work for longs as well. Check this solution of mine for a better and simpler implementation (You should take advantage of the truncating behaviour of C++ int division :)).

Use long long instead of long. Because size of long in codeforces compiler is 4 bytes = ( 2147483648 ). try with below code.

#include <iostream>
int main()
{
    int n = 0;
    std::cin >> n;

    for (int i = 0; i < n; i++)
    {
        long long total = 0;
        long long  a = 0;
        long long b = 0;
        long long c = 0;
        std::cin >> a;
        std::cin >> b;
        std::cin >> c;
        total = a+b+c;
        if (int(total)%2==0)
            std::cout<<total/2 <<"\n";
        else
            std::cout<<(total-1)/2 <<"\n";
        
    }
    return 0;
}