Как сложить целочисленное число типа int с полем класса?

 #include <iostream> 
#include <vector>

using namespace std;

class IntegerValue { 
public: 
    using value_t = int; 
    IntegerValue() : value(0) {} 
    IntegerValue(const value_t value) : value(value) {} 
    IntegerValue& operator+=(const IntegerValue& iv) { 
        this->value += iv.value; 
        return *this; 
    } 
private: 
    value_t value; 
    friend istream& operator>>(istream& inp, IntegerValue& iv) { 
        return inp >> iv.value; 
    } 
    friend ostream& operator<<(ostream& out, const IntegerValue& iv) { 
        return out << iv.value; 
    } 
    friend IntegerValue operator-(const IntegerValue& iv, const value_t value) {
        return IntegerValue(iv.value - value); 
    } 
};

class IntegerCollection { 
public: 
    IntegerCollection(const size_t count) { 
        values.resize(count); 
    } 
    IntegerValue sum(const IntegerValue::value_t discount = 0) const { 
        IntegerValue result = 0; 
        for (const auto& value : values) result += value - discount; 
        return result; 
    } 
private: 
    vector<IntegerValue> values; 
    friend istream& operator>>(istream& inp, IntegerCollection& ic) { 
        for (auto& value : ic.values) inp >> value; 
        return inp; 
    } 
};

int main() { 
    cout << "count: "; 
    size_t count; 
    cin >> count; 
    cout << "array: "; 
    IntegerCollection ic(count); 
    cin >> ic; 
    const auto sum = ic.sum(1); 
    cout << "sum: " << sum << '\n'; 
}