#include <bits/stdc++.h>
using namespace std;
using ll = long long;
#define vi vector<long long>
#define all(x) x.begin(), x.end()
#define endl "\n"
#define pr pair<ll, ll>
#define ff first
#define ss second
void solution();
int main(){
ios::sync_with_stdio(false);
cin.tie(nullptr);
solution();
return 0;
}
ll r, c, d, k;
struct SegTree {
vi lzy, tree;
ll n;
SegTree (ll _n) {
n = _n;
lzy.resize(4*n);
tree.resize(4*n);
}
void push(int id, int l, int r) {
if (!lzy[id]) return;
tree[id] += lzy[id];
if (l != r) {
lzy[2*id] += lzy[id];
lzy[2*id+1] += lzy[id];
}
lzy[id] = 0;
}
void update(int id, int l, int r, int L, int R) {
push(id, l, r);
if (L > r || l > R) return;
if (L <= l && R >= r) {
lzy[id]++;
push(id, l, r);
return;
}
int mid = (l + r)/2;
update(2*id, l, mid, L, R);
update(2*id+1, mid+1, r, L, R);
tree[id] = tree[2*id] + tree[2*id+1];
}
ll query(int id, int l, int r, int pos) {
push(id, l, r);
if (pos < l || pos > r) return 0;
if (l == r) return tree[id];
int mid = (l + r)/2;
return query(2*id, l, mid, pos) + query(2*id+1, mid+1, r, pos);
}
void update(int l, int r) {
l = max(0, l);
r = min(r, int(c-1));
update(1, 0, n-1, l, r);
}
ll query(int pos) {return query(1, 0, n-1, pos);}
};
void solution() {
cin >> r >> c >> d >> k;
string a; cin >> a;
SegTree m(c);
for (int i = 0; i < c; i++) {
if (a[i] == 'S') m.update(i-d, i+d);
}
ll ans = 0;
for (int i = 0; i < c; i++) {
if (a[i] == 'M') ans += (m.query(i) >= k);
}
cout << ans << endl;
}
