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

int main(void) {
    int N;
    if (scanf("%d", &N) != 1) return 0;

    if (N <= 0) {
        printf("Invalid input\n");
        return 0;
    }
    char strs[100][101];
    for (int i = 0; i < N; ++i) {
        if (scanf("%100s", strs[i]) != 1) {
            printf("Invalid input\n");
            return 0;
        }
    }
    int minLen = strlen(strs[0]);
    for (int i = 1; i < N; ++i) {
        int len = strlen(strs[i]);
        if (len < minLen) minLen = len;
    }
    int commonLen = 0;
    for (int pos = 0; pos < minLen; ++pos) {
        char c = strs[0][pos];
        int allSame = 1;
        for (int i = 1; i < N; ++i) {
            if (strs[i][pos] != c) {
                allSame = 0;
                break;
            }
        }
        
}