What is the output of this program?

    #include <iostream>
    using namespace std;
    int add(int a, int b);
    int main()
    {
        int i = 5, j = 6;
        cout << add(i, j) << endl;
        return 0;
    }
    int add(int a, int b )
    {
        int sum = a + b;
        a = 7;
        return a + b;
    }