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

int solution(int* nums, int numsSize, int original) {
    // Simple approach using array as hash table for small numbers
    // For general case, would need proper hash table implementation
    int maxVal = 0;
    for (int i = 0; i < numsSize; i++) {
        if (nums[i] > maxVal) maxVal = nums[i];
    }
    
    if (maxVal <= 0) return original;
    
    int* present = (int*)calloc(maxVal + 1, sizeof(int));
    for (int i = 0; i < numsSize; i++) {
        if (nums[i] >= 0 && nums[i] <= maxVal) {
            present[nums[i]] = 1;
        }
    }
    
    int current = original;
    while (current >= 0 && current <= maxVal && present[current]) {
        current *= 2;
    }
    
    free(present);
    return current;
}

int main() {
    char line[10000];
    fgets(line, sizeof(line), stdin);
    
    // Parse array
    int nums[1000];
    int numsSize = 0;
    char* token = strtok(line + 1, ",]");
    while (token != NULL) {
        nums[numsSize++] = atoi(token);
        token = strtok(NULL, ",]");
    }
    
    int original;
    scanf("%d", &original);
    
    int result = solution(nums, numsSize, original);
    printf("%d\n", result);
    return 0;
}