/**
 * @brief ユーザ定義リテラル
 * @author えびちゃん
 */

#ifndef H_int_literals
#define H_int_literals

#include <cstddef>
#include <cstdint>

constexpr intmax_t  operator ""_jd(unsigned long long n) { return n; }
constexpr uintmax_t operator ""_ju(unsigned long long n) { return n; }
constexpr size_t    operator ""_zu(unsigned long long n) { return n; }
constexpr ptrdiff_t operator ""_td(unsigned long long n) { return n; }

#endif  /* !defined(H_int_literals) */

/**
 * @brief 単一更新セグメント木
 * @author えびちゃん
 */

#ifndef H_basic_segment_tree
#define H_basic_segment_tree

#include <cstddef>
#include <vector>

template <typename Monoid>
class basic_segment_tree {
public:
  using value_type = Monoid;
  using size_type = size_t;

private:
  std::vector<value_type> M_c;
  size_type M_n;

  std::vector<size_type> M_covering_segments(size_type l, size_type r) const {
    std::vector<size_type> left, right;
    l += M_n;
    r += M_n;
    while (l < r) {
      if (l & 1) left.push_back(l++);
      if (r & 1) right.push_back(--r);
      l >>= 1;
      r >>= 1;
    }
    left.insert(left.end(), right.rbegin(), right.rend());
    return left;
  }

public:
  basic_segment_tree() = default;
  basic_segment_tree(basic_segment_tree const&) = default;
  basic_segment_tree(basic_segment_tree&&) = default;

  explicit basic_segment_tree(size_type n): M_c(n+n), M_n(n) {}
  explicit basic_segment_tree(size_type n, value_type const& x):
    M_c(n+n, x), M_n(n)
  {
    for (size_type i = n; i--;) M_c[i] = M_c[i<<1|0] + M_c[i<<1|1];
  }

  template <typename InputIt>
  basic_segment_tree(InputIt first, InputIt last) {
    std::vector<value_type> tmp(first, last);
    M_n = tmp.size();
    M_c.resize(M_n);
    M_c.insert(M_c.end(), tmp.begin(), tmp.end());
    for (size_type i = M_n; i--;) M_c[i] = M_c[i<<1|0] + M_c[i<<1|1];
  }

  void assign(size_type n, value_type const& x) {
    M_c.assign(n+n, x);
    M_n = n;
    for (size_type i = n; i--;) M_c[i] = M_c[i<<1|0] + M_c[i<<1|1];
  }

  template <typename InputIt>
  void assign(InputIt first, InputIt last) {
    std::vector<value_type> tmp(first, last);
    M_n = tmp.size();
    M_c.resize(M_n);
    M_c.insert(M_c.end(), tmp.begin(), tmp.end());
    for (size_type i = M_n; i--;) M_c[i] = M_c[i<<1|0] + M_c[i<<1|1];
  }

  void modify(size_type i, value_type const& x) {
    i += M_n;
    M_c[i] = x;
    while (i > 1) {
      i >>= 1;
      M_c[i] = M_c[i<<1|0] + M_c[i<<1|1];
    }
  }

  void modify(size_type i, value_type&& x) {
    i += M_n;
    M_c[i] = std::move(x);
    while (i > 1) {
      i >>= 1;
      M_c[i] = M_c[i<<1|0] + M_c[i<<1|1];
    }
  }

  value_type const& operator [](size_type i) const { return M_c[i + M_n]; }

  value_type fold(size_type l, size_type r) const {
    value_type resl{}, resr{};
    l += M_n;
    r += M_n;
    while (l < r) {
      if (l & 1) resl += M_c[l++];
      if (r & 1) resr = M_c[--r] + std::move(resr);
      l >>= 1;
      r >>= 1;
    }
    return resl += resr;
  }

  template <typename Predicate>
  size_type partition_point(size_type l, Predicate pred) const {
    if (l == M_n) return l;
    value_type x{};
    size_type v = M_n + M_n;
    std::vector<size_type> cs = M_covering_segments(l, M_n);

    // search the subroot
    for (auto s: cs) {
      if (!pred(x + M_c[s])) {
        v = s;
        break;
      }
      x += M_c[s];
    }

    // search the leaf
    while (v < M_n) {
      v <<= 1;
      if (pred(x + M_c[v])) {
        x += M_c[v];
        v |= 1;
      }
    }

    return v - M_n;
  }
};

#endif  /* !defined(H_basic_segment_tree) */

#include <cstdio>
#include <cstdint>
#include <algorithm>
#include <numeric>
#include <string>
#include <tuple>
#include <utility>
#include <vector>

int main() {
  size_t n;
  scanf("%zu", &n);

  char buf[524288];
  scanf("%s", buf);
  std::string s = buf;

  size_t q;
  scanf("%zu", &q);

  size_t const sigma = 26;
  std::vector<basic_segment_tree<int>> seg(sigma, basic_segment_tree<int>(n));

  for (size_t i = 0; i < n; ++i)
    seg[s[i]-'a'].modify(i, 1);

  for (size_t i = 0; i < q; ++i) {
    int t;
    scanf("%d", &t);

    if (t == 1) {
      // s[j] <- c
      size_t j;
      char c;
      scanf("%zu %c", &j, &c);
      --j;
      seg[s[j]-'a'].modify(j, 0);
      seg[c-'a'].modify(j, 1);
      s[j] = c;
    } else if (t == 2) {
      // [l, r]
      size_t l, r;
      scanf("%zu %zu", &l, &r);
      --l, --r;
      int res = 0;
      for (size_t j = 0; j < sigma; ++j) {
        if (seg[j].fold(l, r+1) > 0) ++res;
      }
      printf("%d\n", res);
    }
  }
}


Measured memory_bytes: 106752