#include <bits/stdc++.h>
using namespace std;
using ll = long long;

const ll base = (1<<18);
ll n, m, tree[2*base];

struct Osoba
{
    ll pos, ile;
};
vector<Osoba> men;

ll query(ll v)
{
    v+=base;
    ll ans = tree[v];
    while(v/=2)
    {
        ans+=tree[v];
    }
    return ans;
}

void add(ll a, ll b, ll l=1, ll r=base, ll v=1)
{
    if(r<a || b<l) return;
    else if(a<=l && r<=b) tree[v]++;
    else
    {
        add(a,b,l,(l+r)/2,2*v);
        add(a,b,(l+r)/2+1,r,2*v+1);
    }
}

ll binsearch(ll x)
{
    ll l=-1, r=men.size()-1, sr;
    while(l+1<r)
    {
        sr = (l+r)/2;
        if(men[sr].pos<x) l = sr;
        else r = sr;
    }
    return r;
}

int32_t main()
{   
    ios_base::sync_with_stdio(0), cin.tie(0);

    cin>>n>>m;
    string s; ll ilem=0, ilek=0, ilemen=0;
    for(ll k, itr=0;itr<m;itr++)
    {
        cin>>s>>k;
        ll temp = 0;
        for(ll i=0;i<s.size();i++) 
        {
            if(s[i]=='M')
            {
                temp++;
                men.push_back({i,i-temp+1});
            }
        }
        ilemen+=temp*k;
    }

    if(ilemen>n)
    {
        cout<<-1;
        return 0;
    }

    for(ll i=0;i<s.size();i+=2)
    {
        if(s[i]=='M') ilem++;
        else ilek++;
        if(s[i+1]=='M') ilem++;
        else ilek++;

        if(ilek-ilem > 2*(n-ilemen))
        {
            ll x = binsearch(i+1);
            add(ilek, men[x].ile);
            ilem++; ilek--;
            s[men[x].pos] = 'F';
            s[i] = 'M';
            men[x].pos=i; men[x].ile=ilek;
        }
    }

    ll ans = 0;
    for(ll i=1;i<=ilek;i++)
    {
        ans = max(ans,query(i));
    }

    cout<<ans;
    // cout<<"\n"<<s;

    return 0;
}