#pragma GCC optimize ("O3")
#pragma GCC target ("sse4")

#include <bits/stdc++.h>
#include <ext/pb_ds/tree_policy.hpp>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/rope>

using namespace std;
using namespace __gnu_pbds;
using namespace __gnu_cxx;
 
typedef long long ll;
typedef long double ld;
typedef complex<ld> cd;

typedef pair<int, int> pi;
typedef pair<ll,ll> pl;
typedef pair<ld,ld> pd;

typedef vector<int> vi;
typedef vector<ld> vd;
typedef vector<ll> vl;
typedef vector<pi> vpi;
typedef vector<pl> vpl;
typedef vector<cd> vcd;

template <class T> using Tree = tree<T, null_type, less<T>, rb_tree_tag,tree_order_statistics_node_update>;

#define FOR(i, a, b) for (int i = (a); i < (b); i++)
#define F0R(i, a) for (int i = 0; i < (a); i++)
#define FORd(i,a,b) for (int i = (b)-1; i >= (a); i--)
#define F0Rd(i,a) for (int i = (a)-1; i >= 0; i--)
#define trav(a, x) for (auto& a : x)

#define mp make_pair
#define pb push_back
#define f first
#define s second
#define lb lower_bound
#define ub upper_bound

#define sz(x) (int)x.size()
#define beg(x) x.begin()
#define en(x) x.end()
#define all(x) beg(x), en(x)
#define resz resize

const int MOD = 1000000007; // 998244353
const ll INF = 1e18;
const int MX = 100001;
const ld PI = 4*atan((ld)1);

template<class T> void ckmin(T &a, T b) { a = min(a, b); }
template<class T> void ckmax(T &a, T b) { a = max(a, b); }

template<class A, class B> A operator+=(A& l, const B& r) { return l = l+r; }
template<class A, class B> A operator-=(A& l, const B& r) { return l = l-r; }
template<class A, class B> A operator*=(A& l, const B& r) { return l = l*r; }
template<class A, class B> A operator/=(A& l, const B& r) { return l = l/r; }

namespace input {
    template<class T> void re(complex<T>& x);
    template<class T1, class T2> void re(pair<T1,T2>& p);
    template<class T> void re(vector<T>& a);
    template<class T, size_t SZ> void re(array<T,SZ>& a);

    template<class T> void re(T& x) { cin >> x; }
    void re(double& x) { string t; re(t); x = stod(t); }
    void re(ld& x) { string t; re(t); x = stold(t); }
    template<class Arg, class... Args> void re(Arg& first, Args&... rest) { 
        re(first); re(rest...); 
    }

    template<class T> void re(complex<T>& x) { T a,b; re(a,b); x = cd(a,b); }
    template<class T1, class T2> void re(pair<T1,T2>& p) { re(p.f,p.s); }
    template<class T> void re(vector<T>& a) { F0R(i,sz(a)) re(a[i]); }
    template<class T, size_t SZ> void re(array<T,SZ>& a) { F0R(i,SZ) re(a[i]); }
}

using namespace input;

namespace output {
    template<class T1, class T2> void pr(const pair<T1,T2>& x);
    template<class T, size_t SZ> void pr(const array<T,SZ>& x);
    template<class T> void pr(const vector<T>& x);
    template<class T> void pr(const set<T>& x);
    template<class T1, class T2> void pr(const map<T1,T2>& x);

    template<class T> void pr(const T& x) { cout << x; }
    template<class Arg, class... Args> void pr(const Arg& first, const Args&... rest) { 
        pr(first); pr(rest...); 
    }

    template<class T1, class T2> void pr(const pair<T1,T2>& x) { 
        pr("{",x.f,", ",x.s,"}"); 
    }
    template<class T> void prContain(const T& x) {
        pr("{");
        bool fst = 1; trav(a,x) pr(!fst?", ":"",a), fst = 0; 
        pr("}");
    }
    template<class T, size_t SZ> void pr(const array<T,SZ>& x) { prContain(x); }
    template<class T> void pr(const vector<T>& x) { prContain(x); }
    template<class T> void pr(const set<T>& x) { prContain(x); }
    template<class T1, class T2> void pr(const map<T1,T2>& x) { prContain(x); }
    
    void ps() { pr("\n"); } 
    template<class Arg, class... Args> void ps(const Arg& first, const Args&... rest) { 
        pr(first," "); ps(rest...); // print w/ spaces
    }
}

using namespace output;

namespace io {
    void setIn(string s) { freopen(s.c_str(),"r",stdin); }
    void setOut(string s) { freopen(s.c_str(),"w",stdout); }
    void setIO(string s = "") {
        ios_base::sync_with_stdio(0); cin.tie(0); // fast I/O
        if (sz(s)) { setIn(s+".in"), setOut(s+".out"); } // for USACO
    }
}

using namespace io;

template<class T> T invGeneral(T a, T b) {
    a %= b; if (a == 0) return b == 1 ? 0 : -1;
    T x = invGeneral(b,a); 
    return x == -1 ? -1 : ((1-(ll)b*x)/a+b)%b;
}

template<class T> struct modInt {
    T val;
    T mod = 0;
    // static const T mod = MOD;

    void normalize() {
        if (mod == 0) return;
        val %= mod; if (val < 0) val += mod;
    }
    modInt(T v = 0, T m = 0) : val(v), mod(m) { normalize(); }
    // modInt(T v = 0, T m = 0) : val(v) { normalize(); }

    explicit operator T() const { return val; }
    friend ostream& operator<<(ostream& os, const modInt& a) { return os << a.val; }
    friend bool operator==(const modInt& a, const modInt& b) { return a.val == b.val; }
    friend bool operator!=(const modInt& a, const modInt& b) { return !(a == b); }

    friend void check(modInt& a, modInt& b) { // make sure all operations are valid
        // comment out if mod is static const
        if (a.mod > 0 && b.mod > 0) { assert(a.mod == b.mod); return; }
        T mod = max(a.mod,b.mod); if (mod == 0) mod = MOD;
        if (a.mod != mod) { a.mod = mod; a.normalize(); }
        if (b.mod != mod) { b.mod = mod; b.normalize(); }
    }
    friend modInt operator+(modInt a, modInt b) {
        check(a,b); a.val += (T)b;
        if (a.val >= a.mod) a.val -= a.mod;
        return a;
    }
    friend modInt operator-(modInt a, modInt b) {
        check(a,b); a.val -= (T)b; 
        if (a.val < 0) a.val += a.mod; 
        return a;
    }
    friend modInt operator-(const modInt& a) { return modInt(0)-a; }

    friend modInt operator*(modInt a, modInt b) {
        check(a,b); a.val = (ll)a.val*(T)b%a.mod; return a;
    }
    friend modInt exp(modInt a, ll p) {
        modInt ans(1,a.mod);
        for (; p; p /= 2, a *= a) if (p&1) ans *= a;
        return ans;
    }
    friend modInt inv(const modInt& a) {
        return {invGeneral(a.val,a.mod),a.mod};
        // return exp(b,b.mod-2) if prime
    }
    friend modInt operator/(modInt a, modInt b) { 
        check(a,b); return a*inv(b); 
    }
};

typedef modInt<int> mi;
typedef pair<mi,mi> pmi;
typedef vector<mi> vmi;
typedef vector<pmi> vpmi;

int N,K, clen;
mi comb[200][200];
vector<vi> v;
vi cur;
string s;

void gen(int lst) {
    // if (lst == 3) ps("??");
    v.pb(cur);
    for (int i = lst; ; ++i) {
        int c = clen; if (c) c ++;
        int len = max(1,2*i-3);
        if (c+len > N) return;
        clen = c+len; cur.pb(i); gen(i);
        clen = c; if (clen) clen --; cur.pop_back();
    } 
}

bool ok(vi needR) {
    deque<int> needB; int need = 0;
    trav(c,s) {
        if (c == 'r') {
            if (sz(needR)) {
                int x = needR.back()-1; needR.pop_back();
                if (x) needB.pb(x);
            } else if (need) need --; 
        } else {
            if (sz(needB)) {
                int x = needB.front()-1; needB.pop_front();
                need += x;
            } else if (need) need --;
        }
    }
    // ps("")
    return !sz(needR) && !sz(needB) && !need;
}

int main() {
    comb[0][0] = 1;
    FOR(i,1,200) {
        comb[i][0] = 1;
        FOR(j,1,i+1) comb[i][j] = comb[i-1][j-1]+comb[i-1][j];
    }
    setIO(); re(N,K,s);
    gen(1);
    mi ret(0);
    trav(t,v) {
        if (!sz(t)) ret += 1;
        else {
            int a = sz(t)-1, b = 0, c = sz(t)+1;
            map<int,int> m;
            mi zz(0);
            // a: # at least, b: possible 1+x, c: (1+x+x^2+...)
            trav(x,t) {
                if (x == 1) a++, c++;
                else a += 2*x-3, b += 2, c += 2*x-3;
            }
            F0R(i,b+1) {
                // a+i numbers, (1+x+x^2+...)^{c+i}
                zz += comb[b][i]*comb[N-(a+i)+(c+i-1)][c+i-1];
                // ret += comb[b][i]*comb[N-(a+i)+sz(t)][sz(t)];
            }
            FOR(i,1,sz(t)+1) zz *= i;
            trav(x,t)  {
                m[x] ++;
                zz /= m[x];
            }
            if (ok(t)) ret += zz;
        }
    }
    ps(ret);
}

/* stuff you should look for
    * int overflow, array bounds
    * special cases (n=1?), set tle
    * do smth instead of nothing and stay organized
*/


Measured memory_bytes: 41000