use std::io::prelude::*;
fn main() {
    let mut input = String::new();
    std::io::stdin().read_to_string(&mut input).unwrap();
    const MOD: u64 = 998244353;
    const KMAX: usize = 26;
    const KMAX2: usize = KMAX + 2;
    let mut tokens = input.split_ascii_whitespace();
    let n = tokens.next().unwrap().parse::<usize>().unwrap();
    let m = tokens.next().unwrap().parse::<usize>().unwrap();
    let k = tokens.next().unwrap().parse::<usize>().unwrap();
    let s = tokens.next().unwrap();
    if n < 1 || n != s.len() || n > m || m > 500000 || k < 1 || k > KMAX {
        panic!();
    }
    let mut kbits = 0u32;
    let mut kbc = 0usize;
    let mut dp = [0u64; KMAX2];
    let mut result = 0u64;
    for c in s.bytes() {
        let mut ndp = [0u64; KMAX2];
        let ci = (c - b'a') as usize;
        if ci >= KMAX {
            panic!();
        }
        let same = (kbits & ((1 << ci) - 1)).count_ones() as u64;
		ndp[kbc] += same;
		ndp[kbc + 1] += (ci as u64) - same;
		if (kbits & (1 << ci)) == 0 {
			kbits |= 1 << ci;
			kbc += 1;
		}
		if kbc >= k {
			result += 1;
		}
        for j in 1..=KMAX {
            ndp[j] += (j as u64) * dp[j];
            ndp[j + 1] += ((KMAX - j) as u64) * dp[j];
            ndp[j] %= MOD;
        }
        for &je in ndp[k..=KMAX].iter() {
            result += je;
        }
        dp = ndp;
    }
    if kbc >= k {
        result -= 1;
    }
    for _ in n..m {
        let mut ndp = [0u64; KMAX2];
        for j in 1..=KMAX {
            ndp[j] += (j as u64) * dp[j];
            ndp[j + 1] += ((KMAX - j) as u64) * dp[j];
            ndp[j] %= MOD;
        }
        for &je in ndp[k..=KMAX].iter() {
            result += je;
        }
        dp = ndp;
    }
    result %= MOD;
    println!("{}", result);
}