#include <iostream>
#include <cmath>

using namespace std;

struct Isotope
{
    int A{};
    int Z{};
};

float empiricalMass(Isotope iso) {
    int N = iso.A - iso.Z;
    int delta = -1;

    if (iso.A % 2 != 0) {
        delta = 0; // mixed parity
    } else if (iso.Z % 2 == 0 && N % 2 == 0) {
        delta = 1; // even-even parity
    }

    float B = 15.75 * iso.A - 94.8 * pow((iso.A/2. - iso.Z), 2.) / iso.A
            - 17.8 * pow(iso.A, 2./3.) - 0.71 * pow(iso.Z, 2.) * pow(iso.A, -1./3.)
            + 34 * delta * pow(iso.A, -3./4.);

    return B/iso.A;
}

int main()
{
    Isotope U235{ 235, 92 };
    float mass = empiricalMass(U235);
    cout << "U235: ";
    cout << mass;
    cout << " MeV per nucleon\n";
    return 0;
}