#include "validation.h"

const int maxn = 100000;
int main() {
	InputValidator v;
	int n = v.read_long_long(1, maxn);
	v.newline();
    string s = v.read_string(n, n);
    for(char c : s) {
        if(c != 'A' && c != 'B' && c != 'C')
            v.WA("String contains non-ABC character.");
    }
	v.newline();
}