#include <bits/stdc++.h>
using namespace std;
 
#define forn(i,n) for(int i=0;i<(int)(n);i++)
#define si(c) ((int)(c).size())
#define forsn(i,s,n) for(int i = (int)(s); i<((int)n); i++)
#define dforsn(i,s,n) for(int i = (int)(n)-1; i>=((int)s); i--)
#define all(c) (c).begin(), (c).end()
#define D(a) cerr << #a << "=" << (a) << endl;
#define pb push_back
#define eb emplace_back
#define mp make_pair
 
typedef long long int ll;
typedef vector<int> vi;
typedef pair<int,int> pii;
mt19937_64 rng(chrono::steady_clock::now().time_since_epoch().count());

const int S = 20;

int n, a, b;
string s;

#define first __nico_first
#define last __nico_last
int sz[1<<S], first[1<<S], last[1<<S];
bool tree[1<<S], forest[1<<S];

bool good(int mask) {
    if (mask == 0) return true;
    int f = first[mask], l = last[mask], c = sz[mask];
    return (l-f+1) * a <= c * b;
}

int main() {
    ios_base::sync_with_stdio(0); cin.tie(0);

    cin >> n >> a >> b;
    cin >> s;
    vi cnt(26), l(26, -1), r(26);
    string t;
    forn(i,n) {
        int d = s[i] - 'a';
        if (cnt[d] == 0) t += s[i];
        cnt[d]++;
        if (l[d] == -1) l[d] = i;
        r[d] = i;
    }

    int k = si(t);
    forn(idx,k) {
        sz[1<<idx] = cnt[t[idx]-'a'];
        first[1<<idx] = l[t[idx]-'a'];
        last[1<<idx] = r[t[idx]-'a'];
    }

    first[0] = n+2;
    forsn(mask, 1, 1<<k) {
        int bit = __builtin_ctz(mask);
        sz[mask] = sz[1<<bit] + sz[mask - (1<<bit)];
        first[mask] = min(first[1<<bit], first[mask - (1<<bit)]);
        last[mask] = max(last[1<<bit], last[mask - (1<<bit)]);
    }

    tree[0] = forest[0] = 1;
    forsn(mask, 1, 1<<k) {
        forn(i,k) if ((mask>>i)&1) {
            tree[mask] |= good(mask) && forest[mask - (1<<i)];
        }
        int prefix = 0, suffix = mask;
        forn(i,k) if ((mask>>i)&1) {
            prefix += 1<<i;
            suffix -= 1<<i;
            forest[mask] |= tree[prefix] && forest[suffix];
        }
    }

    string ans;
    int ALL = (1<<k)-1;
    forn(i,k) if (forest[ALL - (1<<i)]) ans += t[i];

    sort(all(ans));
    cout << si(ans);
    for (auto x : ans) cout << " " << x;
    cout << endl;
    
    return 0;
}
