#include <bits/stdc++.h>
//#include <atcoder/all>
using namespace std;
//using namespace atcoder;
//using mint = modint1000000007;
//const int mod = 1000000007;
//using mint = modint998244353;
//const int mod = 998244353;
//const int INF = 1e9;
//const long long LINF = 1e18;
#define rep(i, n) for (int i = 0; i < (n); ++i)
#define rep2(i,l,r)for(int i=(l);i<(r);++i)
#define rrep(i, n) for (int i = (n) - 1; i >= 0; --i)
#define rrep2(i,l,r)for(int i=(r) - 1;i>=(l);--i)
#define all(x) (x).begin(),(x).end()
#define allR(x) (x).rbegin(),(x).rend()
#define P pair<int,int>
template<typename A, typename B> inline bool chmax(A & a, const B & b) { if (a < b) { a = b; return true; } return false; }
template<typename A, typename B> inline bool chmin(A & a, const B & b) { if (a > b) { a = b; return true; } return false; }
template <class T, class F>
T binarySearch(T ok, T ng, const F &f) {
while (abs(ok - ng) > 1) {
T mid = (ok + ng) / 2;
(f(mid) ? ok : ng) = mid;
}
return ok;
}
int main() {
std::ios::sync_with_stdio(false);
std::cin.tie(nullptr);
int n, a, b; cin >> n >> a >> b;
string s; cin >> s;
vector<int>ca(n + 1), cb(n + 1);
rep(i, n) {
ca[i + 1] = ca[i];
cb[i + 1] = cb[i];
if (s[i] == 'a')ca[i + 1]++;
else cb[i + 1]++;
}
long long ans = 0;
rep(i, n) {
auto f = [&](const long long x)->bool {
int cnt = ca[x] - ca[i];
return cnt >= a;
};
auto g = [&](const long long x)->bool {
int cnt = cb[x] - cb[i];
return cnt < b;
};
if (!f(n))continue;
auto ia = binarySearch<int>(n, i, f) - 1;//l
auto ib = binarySearch<int>(i, n + 1, g);//r
//cout << i << " " << ia << " " << ib << endl;
// if (ib < ia)continue;
ans += max(0, ib - ia);
}
cout << ans << endl;
return 0;
}