#include <iostream>
using namespace std;


int main() {
    char arr[1100] = { 0 };
    cin >> arr;
    int len = strlen(arr);
    int a[130] = { 0 };
    for (int i = 0; i < len; i++){
        a[arr[i]]++;
    }
    for (int i = 0; i < len; i++) {
        if (a[arr[i]] == 1) {
            cout << arr[i] << endl;
            break;
        }
    }
    return 0;
}