#include <iostream>
#include <cstring>
using namespace std;

void lowerCase(char line[]) {
    for (int i = 0; line[i] != '\0'; ++i) {
        if (line[i] >= 'A' && line[i] <= 'Z') {
            line[i] = line[i] + ('a' - 'A');
        }
    }
}

char findMostFrequentLowercase(char text[]) {
    const int ALPHABET_SIZE = 26;
    int letterFrq[ALPHABET_SIZE] = {0};
    for (int i = 0; text[i] != '\0'; ++i) {
        if (text[i] >= 'a' && text[i] <= 'z') {
            letterFrq[text[i] - 'a']++;
        }
    }
    char mostFrequentChar = 0;
    int maxCount = 0;
    for (int i = 0; i < ALPHABET_SIZE; ++i) {
        if (letterFrq[i] > maxCount) {
            maxCount = letterFrq[i];
            mostFrequentChar = 'a' + i;
        }
    }
    return mostFrequentChar;
}

const int MAX_SIZE = 256;

int main() {
    char line[MAX_SIZE + 1], allText[MAX_SIZE + 1] = "";
    int allTextLength = 0;
    while (cin.getline(line, MAX_SIZE + 1)) {
        if (strlen(line) == 0) {
            break;
        }
        lowerCase(line);
        /*for (int i = 0; line[i] != '\0'; ++i) {
            allText[allTextLength++] = line[i];
        }
    }
    allText[allTextLength] = '\0';*/
        strcat(allText, line);
    }
    char mostFrequent = findMostFrequentLowercase(allText);
    cout << mostFrequent << endl;
    return 0;
}