// editor1
#include <stdio.h>
#include <string.h>

void findLongestCommonPrefix(char arr[][100], int n) {
    if (n == 0) {
        printf("Invalid input");
        return;
    }
    
    char prefix[100];
    strcpy(prefix, arr[0]);
    
    for (int i =1; i < n; i++) {
        int j = 0;
        while (j < strlen(prefix) && j < strlen(arr[i]) && prefix[j] = arr[i]) {
            j++;
        }
        prefix[j] = '?';    
    }
    
    if (strlen(prefix) == 0) {
        printf("Invalid input");
    } else {
        printf("%s",prefix);
    }
}

int main() {
    int n;
    printf("Enter the number of strings: ");
    scanf("%d", &n);
    
    char arr[n][100];
    printf("Enter the strings:");
    for (int i = 0; i < n; i++) {
        scanf("%s", arr[i]);
    }
    
    findLongestCommonPrefix(arr, n);
    
    return 0;
}