#include <iostream>
#include <algorithm>
#include <string>
#include <cstdint>
 
//大文字アルファベット縛り。
 
bool MakeHoge(std::string S) {
	std::string X = S;
	std::intmax_t c = 0;
	std::sort(X.begin(), X.end());
	for (auto& o : X) {
		if (o - 'A' == c) { c++; }
		else {
			std::cout <<S<<" => "<< static_cast<char>('A' + c) << std::endl;
			return true;
		}
	}
	return false;
}
 
int main() {
	std::string S;
 
	S = "BCDEFGHIJKLMNOPQRSTUVWXYZ";
	MakeHoge(S);
 
	S = "YIZFOADLMWCRUTGSVQKJEHNBP";
	MakeHoge(S);
 
	return 0;
}
 

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