e.cpp

#include <cstdio>
#include <string>
#include <algorithm>

using namespace std;

bool block(int k1, int locked1, int k2, int locked2)
{
    return (locked1 & (1 << k2));
}

bool dead_lock(int k1, int locked1, int k2, int locked2)
{
    return (locked1 & (1 << k2)) && (locked2 & (1 << k1));
}

bool p[10][1 << 10];

bool safe(const string &s)
{
    fill(&p[0][0], &p[10][0], false);

    int locked = 0;
    for (int i = 0; i < s.size(); ++i) {
        if (s[i] == 'u') {
            locked = 0;
        } else {
            const int k = s[i] - '0';
            if (locked & (1 << k))
                return false;
            p[k][locked] = true;
            locked |= 1 << k;
        }
    }

    /*for (int a = 0; a < 10; ++a)*/ {
        int locked = 0;
        for (int i = 0; i < s.size(); ++i) {
            if (s[i] == 'u') {
                locked = 0;
            } else {
                const int k = s[i] - '0';
                for (int t = 0; t < 10; ++t) {
                    for (int l = 0; l < (1 << 10); ++l) {
                        if (!p[t][l])
                            continue;
                        if (locked & l)
                            continue;
                        if (dead_lock(k, locked, t, l))
                            return false;
                        if (block(k, locked, t, l)) {
                            p[k][locked | l] = true;
                        } else if (block(t, l, k, locked)) {
                            p[t][locked | l] = true;
                        }
                    }
                }
                locked |= 1 << k;
            }
        }
    }

    return true;
}

int main()
{
    for (;;) {
        int n;
        scanf("%d", &n);
        if (n == 0)
            break;
        //fprintf(stderr, "%d\n", n);

        char s[10001];
        scanf("%s", s);

        if (safe(string(s)))
            puts("SAFE");
        else
            puts("UNSAFE");
    }

    return 0;
}