#include <iostream>
#include <cstdio>
#define N 500011
using namespace std;
int book[N];
string a;
char s;
int main()
{
	int n,m;
	cin>>n>>m;
	cin>>a;
    a=' '+a;
	for(int i=1;i<=m;++i)
	{
		string ch;
		int x;
		cin>>ch>>x;
		if(ch[0]=='R') book[x]=1;
		else if(ch[0]=='M') book[x]=2;
	}
    for(int i=1;i<=n;++i)
    {
        if(book[i]==1) a[i]='R';
        else if(book[i]==2) a[i]='M'; 
    }
	if(n==m) a[0]='B';
    for(int i=1;i<=n;++i)
    {
        if(a[i]=='R')
        {
            if(a[i-1]=='B') a[i]='W';
            else if(a[i-1]=='W') a[i]='B';
        }
        if(a[i]=='M')
        {
            if(a[i-1]=='B') a[i]='B';
            else if(a[i-1]=='W') a[i]='W';
        }
    }
    for(int i=n;i>=1;--i)
    {
        if(a[i]=='R')
        {
            if(a[i+1]=='B') a[i]='W';
            else if(a[i+1]=='W') a[i]='B';
        }
        if(a[i]=='M')
        {
            if(a[i+1]=='B') a[i]='B';
            else if(a[i+1]=='W') a[i]='W';
        }
    }
	int ans=0;
	bool check=0;
	for(int i=1;i<=n;++i)
	{
		if(a[i]!=s)
		{
			s=a[i];
			++ans;
			check=1;
		}
	}
	cout<<ans;
	return 0;
}