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



void longest_common_prefix(char *strs[], int n, char *result) {
    // TODO: implement this function
    result[0] = '\0';
}


int main(void) {
    int n;
    if (scanf("%d", &n) != 1) { n = 0; }
    static char bufs[1000][1000];
    char *strs[1000];
    for (int i = 0; i < n; i++) { scanf("%999s", bufs[i]); strs[i] = bufs[i]; }
    char result[1000];
    longest_common_prefix(strs, n, result);
    printf("%s\n", result);
    return 0;
}