#include <algorithm>
#include <cctype>
#include <iostream>
#include <sstream>
#include <string>
 
using namespace std;
 
string solution(string &S){
    const auto n = stoi(S);
    const auto hexaDeciNum = static_cast<ostringstream&>(ostringstream() << hex << uppercase << n).str();
 
    return all_of(cbegin(hexaDeciNum), cend(hexaDeciNum), [](const unsigned char i){ return isxdigit(i); }) ? hexaDeciNum : "ERROR"s;
}
 
int main() {
	auto S = "1234"s;
	cout << solution(S) << endl;
}

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