n, q = map(int, input().split())
s = input()
tds = list(tuple(input().split()) for _ in range(q))

left = 0
right = n-1

for t, d in reversed(tds):
    if d=="L":
        if t==s[left]:
            left = left+1
            if left > n-1:
                right = 0
                break
        if right < n-1 and t==s[right+1]:
            right = min(right+1, n-1)

    if d=="R":
        if t==s[right]:
            right = right-1
            if 0 < right:
                right = 0
                break
        if left > 0 and t==s[left-1]:
            left = max(left-1, 0)

print(max(right - left + 1, 0))
