#include <stdio.h>

int main(int argc, char **argv) {
	int count[26] = { 0 }, first[26] = { 0 };
	int c, i = 0;

	while ((c = getchar()) != EOF) {

		if (c == '\n') {
			int m = 0;
			for (i = 1; i < 26; i++) {
				if (count[i] > count[m]) {
					m = i;
				} else if (count[i] == count[m] && first[i] < first[m]) {
					m = i;
				}
			}

			printf("%c\n", m + 'a');

			for (i = 0; i < 26; i++) {
				count[i] = 0;
				first[i] = 0;
			}
			i = 0;
		} else {
			i++;
			count[c - 'a']++;
			if (!first[c - 'a'])
				first[c - 'a'] = i;
		}

	}

	return 0;
}