#include <stdio.h>
#include <stdlib.h>
#include <string.h>

int solution(int* nums, int numsSize) {
    int left = 0, right = numsSize - 1;
    
    while (left < right) {
        int mid = (left + right) / 2;
        
        // If mid is odd, pair it with previous element
        // If mid is even, pair it with next element
        if (mid % 2 == 1) {
            mid -= 1;
        }
        
        // If the pair is intact, single element is on the right
        if (nums[mid] == nums[mid + 1]) {
            left = mid + 2;
        } else {
            // Pair is broken, single element is on the left (including mid)
            right = mid;
        }
    }
    
    return nums[left];
}

int main() {
    char line[10000];
    fgets(line, sizeof(line), stdin);
    int nums[5000];
    int count = 0;
    char* token = strtok(line, "[],\n");
    while (token != NULL) {
        if (strlen(token) > 0) {
            nums[count++] = atoi(token);
        }
        token = strtok(NULL, "[],\n");
    }
    int result = solution(nums, count);
    printf("%d\n", result);
    return 0;
}