# N, Q = map(int, input().split())
import sys

input = sys.stdin.readline

N, Q = tuple(map(int, input().split()))
s = input()

Query = [input().split() for i in range(Q)]

left, right = 0, N - 1

for t, d in reversed(Query):
    if d == "L":
        if t == s[left]:
            left += 1
        if right < N - 1 and t == s[right + 1]:
            right = min(right + 1, N - 1)
    else:
        if left > 0 and t == s[left - 1]:
            left = max(left - 1, 0)
        if t == s[right]:
            right -= 1
print(max(right - left + 1, 0))
