use std::io::prelude::*;
fn main() {
    let mut input = String::new();
    std::io::stdin().read_to_string(&mut input).unwrap();
    const KMAX: usize = 26;
    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 dp = [MInt(0); KMAX];
    let mut result = MInt(0);
    for c in s.bytes() {
        let mut ndp = [MInt(0); KMAX];
        let ci = (c - b'a') as usize;
        if ci >= KMAX {
            panic!();
        }
        for j in 0..ci {
            let kt = (kbits | (1 << j)).count_ones() - 1;
            ndp[kt as usize] += MInt(1);
        }
        kbits |= 1 << ci;
        if kbits.count_ones() >= (k as u32) {
            result += MInt(1);
        }
        for j in 1..KMAX {
            let je = dp[j - 1];
            ndp[j - 1] += MInt(j as u32) * je;
            ndp[j] += MInt((KMAX - j) as u32) * je;
        }
        ndp[KMAX - 1] += MInt(KMAX as u32) * dp[KMAX - 1];
        for &je in ndp[(k - 1)..KMAX].iter() {
            result += je;
        }
        dp = ndp;
    }
    if kbits.count_ones() >= (k as u32) {
        result -= MInt(1);
    }
    for _ in n..m {
        let mut ndp = [MInt(0); KMAX];
        for j in 1..KMAX {
            let je = dp[j - 1];
            ndp[j - 1] += MInt(j as u32) * je;
            ndp[j] += MInt((KMAX - j) as u32) * je;
        }
        ndp[KMAX - 1] += MInt(KMAX as u32) * dp[KMAX - 1];
        for &je in ndp[(k - 1)..KMAX].iter() {
            result += je;
        }
        dp = ndp;
    }
    println!("{}", result.val());
}
pub trait ModInt32Static {
    const MOD: u32;
    fn norm_impl(n: u32) -> u32;
    fn add_impl(lhs: u32, rhs: u32) -> u32;
    fn sub_impl(lhs: u32, rhs: u32) -> u32;
    fn mul_impl(lhs: u32, rhs: u32) -> u32;
}
macro_rules! modint32static_impl {
    ($modulus:literal, $st:ident) => {
        modint32static_impl!(@dol ($) $modulus, $st);
    };
    (@dol ($dol:tt) $modulus:literal, $st:ident) => {
        #[derive(Copy, Clone)]
        pub struct $st(u32);
        impl ModInt32Static for $st {
            const MOD: u32 = ($modulus as u32);
            #[inline]
            fn norm_impl(x: u32) -> u32 {
                x % Self::MOD
            }
            #[inline]
            fn add_impl(lhs: u32, rhs: u32) -> u32 {
                let v = u64::from(lhs) + u64::from(rhs);
                match v.checked_sub(u64::from(Self::MOD)) {
                    None => v as u32,
                    Some(w) => w as u32,
                }
            }
            #[inline]
            fn sub_impl(lhs: u32, rhs: u32) -> u32 {
                let (v, f) = lhs.overflowing_sub(rhs);
                v.wrapping_add(u32::from(f).wrapping_neg() & Self::MOD)
            }
            #[inline]
            fn mul_impl(lhs: u32, rhs: u32) -> u32 {
                (u64::from(lhs) * u64::from(rhs) % u64::from(Self::MOD)) as u32
            }
        }
        impl std::ops::Add for $st {
            type Output = Self;
            #[inline]
            fn add(self, rhs: Self) -> Self::Output {
                $st($st::add_impl(self.0, rhs.0))
            }
        }
        impl std::ops::Sub for $st {
            type Output = Self;
            #[inline]
            fn sub(self, rhs: Self) -> Self::Output {
                $st($st::sub_impl(self.0, rhs.0))
            }
        }
        impl std::ops::Mul for $st {
            type Output = Self;
            #[inline]
            fn mul(self, rhs: Self) -> Self::Output {
                $st($st::mul_impl(self.0, rhs.0))
            }
        }
        impl std::ops::Neg for $st {
            type Output = Self;
            #[inline]
            fn neg(self) -> Self::Output {
                $st($st::sub_impl(0, self.0))
            }
        }
        impl std::ops::AddAssign for $st {
            #[inline]
            fn add_assign(&mut self, rhs: Self) {
                *self = Self(Self::add_impl(self.0, rhs.0));
            }
        }
        impl std::ops::SubAssign for $st {
            #[inline]
            fn sub_assign(&mut self, rhs: Self) {
                *self = Self(Self::sub_impl(self.0, rhs.0));
            }
        }
        impl std::ops::MulAssign for $st {
            #[inline]
            fn mul_assign(&mut self, rhs: Self) {
                *self = Self(Self::mul_impl(self.0, rhs.0));
            }
        }
        impl $st {
            #[inline]
            pub fn new(n: u32) -> Self {
                Self(Self::norm_impl(n))
            }
            #[inline]
            pub fn val(&self) -> u32 {
                self.0
            }
        }
    };
}
modint32static_impl!(998244353, MInt);