72行代码做出来了

修改了十多次，老是忘记写大括号，没有在相应函数的命名空间里声明（早知道用万能头了）
以下是代码：
#include <iostream>
#include <string>
#include <limits>
#include <stdexcept>
#include <chrono>
#include <climits>
#include <cstdlib>

namespace InputUtils {
bool isInteger(const std::string& s) {
if(s.empty()) return false;
size_t i = (s[0] == '-') ? 1 : 0;
for(; i < s.size(); ++i) {
if(!isdigit(s[i])) return false;
}
return true;
}

int safeConvert(const std::string& s) {
    try {
        size_t pos = 0;
        long val = std::stol(s, &pos);
        if(pos != s.length() || val < INT_MIN || val > INT_MAX) {
            throw std::out_of_range("");
        }
        return static_cast<int>(val);
    } catch(...) {
        throw std::invalid_argument("");
    }
}

}

namespace MathUtils {
int safeAdd(int a, int b) {
if((b > 0 && a > INT_MAX - b) ||
(b < 0 && a < INT_MIN - b)) {
throw std::overflow_error("");
}
return a + b;
}
}

class Timer {
stdchronosteady_clocktime_point start;
public:
Timer() { start = stdchronosteady_clocknow(); }
long elapsed() const {
return stdchronoduration_caststd::chrono::microseconds(
stdchronosteady_clock::now() - start).count();
}
};

int main() {
Timer timer;
stdstring a_str, b_str;
stdcin >> a_str >> b_str;

if(!InputUtils::isInteger(a_str) || !InputUtils::isInteger(b_str)) {
    return EXIT_FAILURE;
}

try {
    int a = InputUtils::safeConvert(a_str);
    int b = InputUtils::safeConvert(b_str);
    int result = MathUtils::safeAdd(a, b);
    std::cout << result;
} catch(...) {
    return EXIT_FAILURE;
}

return EXIT_SUCCESS;

}