#include <bits/stdc++.h>
using namespace std;
const int N = 500005;
const int INF = 1e9;
struct Node {
int sum, val;
Node() { sum = val = 0; }
void dbg() { cout << "#node " << sum << ' ' << val << '\n'; }
};
struct Query {
int l, r, id;
bool operator < (const Query& rhs) const {
return l > rhs.l;
}
};
int n, q, res[N];
string s;
Node T[N * 2];
vector<Query> queries;
Node combine(Node &x, Node &y) {
Node ret;
ret.sum = x.sum + y.sum;
ret.val = min(y.val, x.val + y.sum);
return ret;
}
void upd(int p, int x) {
// cout << "#upd " << p << ' ' << x << '\n';
p += n, T[p].sum = T[p].val = x;
while (p > 1) {
p >>= 1;
T[p] = combine(T[p << 1], T[p << 1 | 1]);
// cout << "#p " << p << '\n';
// T[p].dbg();
}
}
int get(int l, int r) {
// cout << "#get " << l << ' ' << r << '\n';
Node Tl, Tr;
for (l += n, r += n; l <= r; l >>= 1, r >>= 1) {
// cout << l << ' ' << r << '\n';
if (l & 1) Tl = combine(Tl, T[l++]);
if (!(r & 1)) Tr = combine(T[r--], Tr);
}
// Tl.dbg(), Tr.dbg();
return combine(Tl, Tr).val;
}
int main() {
ios::sync_with_stdio(false);
cin >> n >> s >> q, s = ' ' + s;
for (int i = 1; i <= q; ++i) {
int l, r; cin >> l >> r;
queries.push_back({l, r, i});
}
sort(queries.begin(), queries.end());
int ptr = n;
vector<int> vec;
for (auto i : queries) {
while (ptr >= i.l) {
if (s[ptr] == 'T') vec.push_back(ptr);
else {
upd(ptr, 1);
if (vec.size()) {
int p = vec.back();
upd(p, -1), vec.pop_back();
}
}
--ptr;
}
// cout << get(i.l, i.r) << '\n';
res[i.id] = upper_bound(vec.rbegin(), vec.rend(), i.r) - vec.rbegin() - get(i.l, i.r);
}
for (int i = 1; i <= q; ++i) cout << res[i] << '\n';
}
