// ${url}
//
#![allow(unused_imports)]
use std::io::*;
use std::io::Write;
use std::fmt::*;
use std::str::*;
use std::cmp::*;
use std::collections::*;

// Input macros.
// Original by tanakh: https://qiita.com/tanakh/items/0ba42c7ca36cd29d0ac8
#[allow(unused_macros)]
macro_rules! input {
    (source = $s:expr, $($r:tt)*) => {
        let mut iter = $s.split_whitespace();
        input_inner!{iter, $($r)*}
    };
    ($($r:tt)*) => {
        let s = {
            use std::io::Read;
            let mut s = String::new();
            std::io::stdin().read_to_string(&mut s).unwrap();
            s
        };
        let mut iter = s.split_whitespace();
        input_inner!{iter, $($r)*}
    };
}

#[allow(unused_macros)]
macro_rules! input_inner {
    ($iter:expr) => {};
    ($iter:expr, ) => {};

    ($iter:expr, $var:ident : $t:tt $($r:tt)*) => {
        let $var = read_value!($iter, $t);
        input_inner!{$iter $($r)*}
    };

    ($iter:expr, mut $var:ident : $t:tt $($r:tt)*) => {
        let mut $var = read_value!($iter, $t);
        input_inner!{$iter $($r)*}
    };
}

#[allow(unused_macros)]
macro_rules! read_value {
    ($iter:expr, ( $($t:tt),* )) => {
        ( $(read_value!($iter, $t)),* )
    };

    ($iter:expr, [ $t:tt ; $len:expr ]) => {
        (0..$len).map(|_| read_value!($iter, $t)).collect::<Vec<_>>()
    };

    ($iter:expr, [ next / $t:tt ]) => {
        {
            let len = read_value!($iter, usize);
            (0..len).map(|_| read_value!($iter, $t)).collect::<Vec<_>>()
        }
    };

    ($iter:expr, switch) => {
        {
            let ty = read_value!($iter, i32);
            if ty == 1 {
                vec![ty, read_value!($iter, i32), read_value!($iter, i32)]
            } else if ty == 2 {
                vec![ty, read_value!($iter, i32)]
            } else {
                vec![ty, read_value!($iter, i32)]
            }
        }
    };

    ($iter:expr, chars) => {
        read_value!($iter, String).chars().collect::<Vec<char>>()
    };

    ($iter:expr, usize1) => {
        read_value!($iter, usize) - 1
    };

    ($iter:expr, $t:ty) => {
        $iter.next().unwrap().parse::<$t>().expect("Parse error")
    };
}

#[allow(unused_macros)]
macro_rules! read_line {
    ($t:tt) => {
        {
            let mut s = String::new();
            std::io::stdin().read_line(&mut s).unwrap();
            s.trim_right().parse::<$t>().unwrap()
        }
    }
}

#[allow(unused_macros)]
macro_rules! dvec {
    ($t:expr ; $len:expr) => {
        vec![$t; $len]
    };

    ($t:expr ; $len:expr, $($rest:expr),*) => {
        vec![dvec!($t; $($rest),*); $len]
    };
}

#[allow(unused_macros)]
macro_rules! ifv {
    ($t:expr, $a:expr, $b: expr) => {
        if $t { $a } else { $b }
    }
}

#[allow(unused_macros)]
macro_rules! fill {
    ($t:expr, $v:expr) => {
        for i in 0..$t.len() {
            $t[i] = $v;
        }
    };
}

#[allow(unused_macros)]
macro_rules! join {
    ($t:expr, $glue:expr) => {
        $t.into_iter().map(|w| w.to_string()).collect::<Vec<_>>().join($glue)
    };
}

#[allow(unused_macros)]
macro_rules! debug {
    ($($a:expr),*) => {
        eprintln!(concat!($(stringify!($a), " = {:?}, "),*), $($a),*);
    }
}

// ===

fn solve_left(s: &Vec<char>, queries: &Vec<(char, char)>, mut idx: usize) -> bool {
    let n = s.len();
    for &(c, lr) in queries {
        if s[idx] == c {
            if lr == 'L' {
                if idx == 0 {
                    return true;
                }
                idx -= 1;
            } else {
                if idx == n-1 {
                    return false;
                }
                idx += 1;
            }
        }
    }
    false
}


fn solve_right(s: &Vec<char>, queries: &Vec<(char, char)>, mut idx: usize) -> bool {
    let n = s.len();
    for &(c, lr) in queries {
        if s[idx] == c {
            if lr == 'L' {
                if idx == 0 {
                    assert!(false, "Cannot be here");
                }
                idx -= 1;
            } else {
                if idx == n-1 {
                    return true;
                }
                idx += 1;
            }
        }
    }
    false
}

fn main() {
    input! {
        n: usize, q: usize,
        s: chars,
        queries: [(char, char); q]
    };
    let mut fallen = 0;

    // 1 to n
    let mut ok = 0;
    let mut ng = n+1;
    while ng - ok > 1 {
        let med = (ok + ng) / 2;
        if solve_left(&s, &queries, med-1) {
            ok = med;
        } else {
            ng = med;
        }
    }
    fallen = ok;

    let mut ng = ok;
    let mut ok = n+1;
    while ok - ng > 1 {
        let med = (ok + ng) / 2;
        if solve_right(&s, &queries, med-1) {
            ok = med;
        } else {
            ng = med;
        }
    }
    fallen += (n+1)-ok;

    println!("{}", n-fallen);
}


Measured memory_bytes: 5260