#include <bits/stdc++.h>
typedef long long LL;
typedef unsigned long long ULL;
typedef std::pair<int, int> pii;
typedef std::pair<LL, LL> pll;
#define fi first
#define se second
#define MP std::make_pair
#define clr(f, n) memset(f, 0, (n) << 2)
#define cpy(f, g, n) memcpy(f, g, (n) << 2)
#define rev(f, n) std::reverse(f, (f) + (n))
int read() {
    int s = 0, f = 1;
    char c = getchar();
    while (!(c >= '0' && c <= '9')) f ^= (c == '-'), c = getchar();
    while (c >= '0' && c <= '9') s = s * 10 + (c - '0'), c = getchar();
    return f ? s : -s;
}
const int MAXN = 200005, MOD = 998244353;
const int inf = 0x3f3f3f3f;
const LL INF = 4e18;
template <typename T>
T& Fmin(T& x, T y) {
    return x = x < y ? x : y;
}
template <typename T>
T& Fmax(T& x, T y) {
    return x = x < y ? y : x;
}
int fplus(int x, int y) { return x + y >= MOD ? x + y - MOD : x + y; }
int fminus(int x, int y) { return x >= y ? x - y : x + MOD - y; }
int& Fplus(int& x, int y) { return x = fplus(x, y); }
int& Fminus(int& x, int y) { return x = fminus(x, y); }
int fpow(int x, int y = MOD - 2) {
    int res = 1;
    for (; y; y >>= 1, x = (LL)x * x % MOD)
        if (y & 1)
            res = (LL)res * x % MOD;
    return res;
}
int n, a[MAXN], A, B, nxt[MAXN];
LL s1[MAXN], s2[MAXN];
namespace SGT {
int sgt[MAXN * 200], ls[MAXN * 200], rs[MAXN * 200], tot = 0;
void clear() {
    for (; tot; tot--) sgt[tot] = ls[tot] = rs[tot] = 0;
}
void modify(int& x, int l, int r, int pos, int v) {
    if (!x)
        x = ++tot;
    if (l == r)
        return Fmax(sgt[x], v), void();
    int mid = (l + r) >> 1;
    if (pos <= mid)
        modify(ls[x], l, mid, pos, v);
    else
        modify(rs[x], mid + 1, r, pos, v);
    sgt[x] = std::max(sgt[ls[x]], sgt[rs[x]]);
}
int query(int x, int l, int r, int ql, int qr) {
    if (!x)
        return -inf;
    if (ql <= l && r <= qr)
        return sgt[x];
    int mid = (l + r) >> 1, res = -inf;
    if (ql <= mid)
        Fmax(res, query(ls[x], l, mid, ql, qr));
    if (qr > mid)
        Fmax(res, query(rs[x], mid + 1, r, ql, qr));
    return res;
}
}
struct BIT {
    std::vector<int> rt;
    int n;
    void init(int _n) { rt.resize((n = _n) + 1), rt.assign(n + 1, 0); }
    void modify(int x, int pos, int v) {
        for (; x <= n; x += x & -x) SGT::modify(rt[x], 1, n, pos, v);
    }
    int query(int x, int v) {
        int res = ~0x3f3f3f3f;
        for (; x; x -= x & -x) Fmax(res, SGT::query(rt[x], 1, n, v, n));
        return res;
    }
} bit[MAXN];
std::vector<LL> tmp[MAXN];
int f[MAXN];
void calc() {
    int K = A + B;
    for (int r = 0; r <= K; r++) {
        tmp[r].clear();
        for (int i = r; i <= n + 1; i += K) tmp[r].push_back(s1[i - 1]), tmp[r].push_back(s2[i - 1]);
        std::sort(tmp[r].begin(), tmp[r].end());
        int V = std::unique(tmp[r].begin(), tmp[r].end()) - tmp[r].begin();
        tmp[r].resize(V), bit[r].init(V);
    }
    memset(f + 1, ~0x3f, (n + 1) << 2), f[n + 1] = 0;
    SGT::clear();
    for (int i = n + 1; i; i--) {
        int r = i % K;
        int idx = std::lower_bound(tmp[r].begin(), tmp[r].end(), s1[i - 1]) - tmp[r].begin() + 1;
        int idy = std::lower_bound(tmp[r].begin(), tmp[r].end(), s2[i - 1]) - tmp[r].begin() + 1;
        if (i <= n)
            f[i] = std::max(f[i + 1], bit[r].query(idx, idy) - i / K);
        bit[r].modify(idx, idy, f[i] + i / K);
        // printf("%d: %d\n", i, f[i]);
    }
}
char s[MAXN];
void mian() {
    n = read(), A = read(), B = read();
    scanf("%s", s + 1);
    for (int i = 1; i <= n; i++) 
        if (s[i] == 'B') a[i] = 1;
        else if (s[i] == 'W') a[i] = 0;
        else a[i] = -1;
    for (int i = 1; i <= n; i++) {
        s1[i] = s1[i - 1] - A, s2[i] = s2[i - 1] - A;
        if (a[i] == -1) s1[i] += A + B;
        if (a[i] != 1) s2[i] += A + B;
    }
    calc();
    printf("%d\n", f[1]);
}
int main() {
    for (int T = 1; T--;) mian();
    return 0;
}