
// http://judge.u-aizu.ac.jp/onlinejudge/description.jsp?id=1161&lang=jp

#include<iostream>
#include<map>
#include<vector>
#include<algorithm>
#include<cmath>
#include<climits>
#include<ctime>
#include<cstring>
#include<numeric>

#define ALL(v) (v).begin(),(v).end()
#define REP(i,p,n) for(int i=p;i<(int)(n);++i)
#define rep(i,n) REP(i,0,n)
#define dump(a) (cerr << #a << "=" << (a) << endl)
#define DUMP(list) cout << "{ "; for(auto nth : list){ cout << nth << " "; } cout << "}" << endl;

using namespace std;

vector<int> coefficient;
vector<bool> is_top;

int dfs(int m, int depth, int used, int value) {
	if(depth == m) 
		return ((value == 0) ? 1 : 0);

	int ret = 0;
	rep(i, 10) { 
		if(is_top[depth] && i == 0) continue;
		if(used & (1 << i)) continue;
		ret += dfs(m, depth + 1, used | (1 << i), value + coefficient[depth] * i); 
	}
	return ret;
}

int main() {
	int n;
	while(cin >> n, n) {
		map<char, int> converter;
		
		// アルファベットの種類を数える
		vector<string> s(n, "");
		rep(i, n) {
			cin >> s[i];
			rep(j, s[i].size()) {
				if(!converter.count(s[i][j])) converter.insert(make_pair(s[i][j], converter.size()));
			}
		}

		// 各アルファベットの係数と先頭にあるかを求める
		int m = converter.size();
		coefficient.assign(m, 0);
		is_top.assign(m, false);
		rep(i, n) {
			for(int j = s[i].size() - 1, k = 1; j >= 0; --j, k *= 10) {
				int ctoi = converter[s[i][j]];
				if(j == 0 && s[i].size() > 1) is_top[ctoi] = true;
				coefficient[ctoi] +=  (i == n - 1) ? -k : k;
			}
		}
		
		// 覆面算が成り立つ式を満たす組み合わせを探索
		cout << dfs(m, 0, 0, 0) << endl;
	}
	return 0;
}