#include <fstream>
using namespace std;
ifstream f("furnici.in");
ofstream g("furnici.out");
int i,n,maxi,d,l,x;
char c;
int main()
{

    f>>l>>n;
    maxi=-1;
    for(i=1;i<=n;++i)
    {
        f>>x>>c;
        if(c=='S')
        d=x;
        else
        d=l-x;
        if(d>maxi)
        maxi=d;
    }
            g<<maxi;
        return 0;
}