#include <iostream>
#include <random>
#include <bits/stdc++.h>
using namespace std;
using ull = __int128;
using ll = long long;
#define rep(i,a,b) for(int i=a;i<b;i++)
#include <iostream>
using namespace std;

const int MAX = 2000010;
const int mod = 1000000007;
const int MOD = 1000000007;

long long fac[MAX], finv[MAX], inv[MAX];

// テーブルを作る前処理
void COMinit() {
    fac[0] = fac[1] = 1;
    finv[0] = finv[1] = 1;
    inv[1] = 1;
    for (int i = 2; i < MAX; i++){
        fac[i] = fac[i - 1] * i % MOD;
        inv[i] = MOD - inv[MOD%i] * (MOD / i) % MOD;
        finv[i] = finv[i - 1] * inv[i] % MOD;
    }
}

// 二項係数計算
long long COM(int n, int k){
    if (n < k) return 0;
    if (n < 0 || k < 0) return 0;
    return fac[n] * (finv[k] * finv[n - k] % MOD) % MOD;
}

class mint {
    long long x;
public:
    mint(long long x=0) : x((x%mod+mod)%mod) {}
    mint operator-() const { 
      return mint(-x);
    }
    mint& operator+=(const mint& a) {
        if ((x += a.x) >= mod) x -= mod;
        return *this;
    }
    mint& operator-=(const mint& a) {
        if ((x += mod-a.x) >= mod) x -= mod;
        return *this;
    }
    mint& operator*=(const  mint& a) {
        (x *= a.x) %= mod;
        return *this;
    }
    mint operator+(const mint& a) const {
        mint res(*this);
        return res+=a;
    }
    mint operator-(const mint& a) const {
        mint res(*this);
        return res-=a;
    }
    mint operator*(const mint& a) const {
        mint res(*this);
        return res*=a;
    }
    mint pow(ll t) const {
        if (!t) return 1;
        mint a = pow(t>>1);
        a *= a;
        if (t&1) a *= *this;
        return a;
    }
    // for prime mod
    mint inv() const {
        return pow(mod-2);
    }
    mint& operator/=(const mint& a) {
        return (*this) *= a.inv();
    }
    mint operator/(const mint& a) const {
        mint res(*this);
        return res/=a;
    }

    friend ostream& operator<<(ostream& os, const mint& m){
        os << m.x;
        return os;
    }
  friend istream& operator>>(istream& lhs,mint& rhs) noexcept {
        lhs >> rhs.x;
        return lhs;
    }
};
ll modmul(ll x, ll y, ll mod){
	ll ret = 0;
	while(y){
		if(y & 1){
			ret = (ret + x) % mod;
		}
		x = x * 2 % mod;
		y >>= 1;
	}
	return ret;
}

ll modpow(ll x, ll n, ll mod){
	ll ret = 1;
	while(n){
		if(n & 1){
			ret = modmul(ret, x, mod);
		}
		x = modmul(x, x, mod);
		n >>= 1;
	}
	return ret;
}

int main() {
    // 前処理
    COMinit();
ll a;
  cin>>a;
  ll b;
  cin>>b;
  string c;
  cin>>c;
  ll d=0;
  ll e=0;
 for(int i=0;i<ll(c.size());i++){
   if(c.at(i)=='-'){
     d++;
   }
   else{
     e++;
   }
 }
   ll f=a-b;
   mint ans=0;
   mint k=1;
   for(int i=2;i<d;i++){
     k=k*i;
   }
   for(int i=d;i<=a-e;i++){
     if(i!=0){
       k=k*i;
     }
     ans=ans+mint(mint(mint(COM(f,i-d))*k)*modpow(a,a-i,mod));
 }
 cout<<mint(mint(f+1)*ans)<<endl;
}