//  ____            _                  _                       _       _
// |  _ \ _   _ ___| |_    ___ _ __   | |_ ___ _ __ ___  _ __ | | __ _| |_ ___
// | |_) | | | / __| __|  / __| '_ \  | __/ _ \ '_ ` _ \| '_ \| |/ _` | __/ _ \
// |  _ <| |_| \__ \ |_  | (__| |_) | | ||  __/ | | | | | |_) | | (_| | ||  __/
// |_| \_\\__,_|___/\__|  \___| .__/___\__\___|_| |_| |_| .__/|_|\__,_|\__\___|
//                            |_| |_____|               |_|

//https://github.com/manta1130/Competitive_Programming_Template_Rust

#[macro_use]
mod input {

    use std;
    use std::io;

    const SPLIT_DELIMITER: char = ' ';

    #[macro_export]
    #[allow(unused_macros)]
    macro_rules! input {
    ( $($x:expr ),*) => {
        {
            let temp_str = input_line_str();
            let mut split_result_iter = temp_str.split_whitespace();
                $(
                let buf_split_result = split_result_iter.next();
                let buf_split_result = buf_split_result.unwrap();
                    ($x) = buf_split_result.parse().unwrap();
                )*
        }
    };
}

    #[allow(dead_code)]
    pub fn input_line_str() -> String {
        let mut s = String::new();
        io::stdin().read_line(&mut s).unwrap();
        s.trim().to_string()
    }

    #[allow(dead_code)]
    pub fn p<T>(t: T)
    where
        T: std::fmt::Display,
    {
        println!("{}", t);
    }

    #[allow(dead_code)]
    pub fn input_vector2d<T>(line: usize) -> Vec<Vec<T>>
    where
        T: std::str::FromStr,
    {
        let mut v: Vec<Vec<T>> = Vec::new();

        for _ in 0..line {
            let vec_line = input_vector();
            v.push(vec_line);
        }
        v
    }

    #[allow(dead_code)]
    pub fn input_vector<T>() -> Vec<T>
    where
        T: std::str::FromStr,
    {
        let mut v: Vec<T> = Vec::new();

        let s = input_line_str();
        let split_result = s.split(SPLIT_DELIMITER);
        for z in split_result {
            let buf = match z.parse() {
                Ok(r) => r,
                Err(_) => panic!("Parse Error"),
            };
            v.push(buf);
        }
        v
    }

    #[allow(dead_code)]
    pub fn input_vector_row<T>(n: usize) -> Vec<T>
    where
        T: std::str::FromStr,
    {
        let mut v = Vec::with_capacity(n);
        for _ in 0..n {
            let buf = match input_line_str().parse() {
                Ok(r) => r,
                Err(_) => panic!("Parse Error"),
            };
            v.push(buf);
        }
        v
    }

    pub trait ToCharVec {
        fn to_charvec(&self) -> Vec<char>;
    }

    impl ToCharVec for String {
        fn to_charvec(&self) -> Vec<char> {
            self.to_string().chars().collect::<Vec<_>>()
        }
    }
}

use input::*;
use std::collections::{HashMap, HashSet};

fn main() {
    let n: usize;
    input!(n);
    let mut s = input_line_str().to_charvec();
    let bs = 1000;
    let mut block = vec![vec![0; 26]; n / bs + 10];
    let table = String::from("abcdefghijklmnopqrstuvwxyz");
    let table = table.to_charvec();
    for i in 0..n {
        block[i / bs][table.iter().position(|&x| x == s[i]).unwrap()] += 1;
    }
    let q: usize;
    input!(q);
    for _ in 0..q {
        let z = input_line_str();
        let x = z.to_charvec();
        if x[0] == '1' {
            let p = &z.split(' ').collect::<Vec<&str>>();
            let d = p[1].parse::<usize>().unwrap() - 1;
            let c = p[2].chars().collect::<Vec<_>>();
            let c = c[0];
            block[d / bs][table.iter().position(|&x| x == c).unwrap()] += 1;
            block[d / bs][table.iter().position(|&x| x == s[d]).unwrap()] -= 1;

            s[d] = c;
        } else {
            let p = &z.split(' ').collect::<Vec<&str>>();
            let f = p[1].parse::<usize>().unwrap() - 1;
            let t = p[2].parse::<usize>().unwrap();
            let mut ans = vec![0; 26];
            let mut i = f;
            while i < t {
                if i % bs == 0 && i + bs < t {
                    for l in 0..26 {
                        ans[l] += block[i / bs][l];
                    }
                    i += bs;
                } else {
                    ans[table.iter().position(|&x| x == s[i]).unwrap()] += 1;
                    i += 1;
                    //println!("1");
                }
                //println!("{:?}", &ans);
            }
            println!("{}", ans.iter().filter(|&&x| x != 0).count());
        }
    }
}


Measured memory_bytes: 8444