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

char* solution(char** strs, int strsSize) {
    if (strsSize == 0) {
        char* result = malloc(1);
        result[0] = '\0';
        return result;
    }
    
    int firstLen = strlen(strs[0]);
    
    // Use first string as reference for length
    for (int i = 0; i < firstLen; i++) {
        // Get character at position i from first string
        char c = strs[0][i];
        
        // Check all other strings at position i
        for (int j = 1; j < strsSize; j++) {
            // If string j is too short or character doesn't match
            if (i >= strlen(strs[j]) || strs[j][i] != c) {
                char* result = malloc(i + 1);
                strncpy(result, strs[0], i);
                result[i] = '\0';
                return result;
            }
        }
    }
    
    // All characters in first string match across all strings
    char* result = malloc(firstLen + 1);
    strcpy(result, strs[0]);
    return result;
}

int main() {
    char line[10000];
    fgets(line, sizeof(line), stdin);
    line[strcspn(line, "\n")] = 0;
    
    // Simple parsing for array of strings
    char** strs = malloc(1000 * sizeof(char*));
    int strsSize = 0;
    
    if (strlen(line) > 2) {
        char* token = strtok(line + 1, ",]"); // Skip [ and split by comma
        while (token != NULL) {
            // Remove quotes and spaces
            while (*token == ' ' || *token == '"') token++;
            int len = strlen(token);
            while (len > 0 && (token[len-1] == ' ' || token[len-1] == '"')) {
                token[len-1] = '\0';
                len--;
            }
            strs[strsSize] = malloc(len + 1);
            strcpy(strs[strsSize], token);
            strsSize++;
            token = strtok(NULL, ",]");
        }
    }
    
    char* result = solution(strs, strsSize);
    printf("%s\n", result);
    
    // Cleanup
    for (int i = 0; i < strsSize; i++) {
        free(strs[i]);
    }
    free(strs);
    free(result);
    return 0;
}