#include <iostream>
#include <stdio.h>
#include <string>
using namespace std;

#define checkmin(a,b) if(a>b)a=b
const int INF = 0x4ffffff;

char str[105][105];
int len[105];
int main()
{
	int n,i,j,k;
	while(scanf("%d",&n),n)
	{
		int ans=inf;
		for(i=1;i<=n;i++)
		{
			scanf("%s",str[i]);
			len[i]=strlen(str[i]);
			checkmin(ans,len[i]-1);
		}
		for(i=1;i<=n;i++)for(j=i+1;j<=n;j++)if(len[i]==len[j])
		{
			for(k=len[i]-1;k>=0;k--)if(str[i][k]!=str[j][k])break;
			checkmin(ans,k);
		}
		printf("%d\n",ans);
	}
}