n,q=map(int,input().split())
s=input()
p=[input().split() for i in range(q)]
def judge_l(x):
    for(k,v)in p:
        if k==s[x]:
            if v=="L":
                x-=1
            else:
                x+=1
        if x==-1:
            return True
        elif x==n:
            return False
    return False

def judge_r(x):
    for(k,v)in p:
        if k==s[x]:
            if v=="L":
                x-=1
            else:
                x+=1
        if x==-1:
            return False
        elif x==n:
            return True
    return False

ok=-1
ng=n

while abs(ok-ng)>1:
    mid=(ok+ng)//2
    if judge_l(mid):
        ok=mid
    else:
        ng=mid
l=ok+1

ok=n
ng=-1

while abs(ok-ng)>1:
    mid=(ok+ng)//2
    if judge_r(mid):
        ok=mid
    else:
        ng=mid
r=n-ok
#print(l,r)
print(max(n-l-r,0))