import std.conv, std.functional, std.range, std.stdio, std.string;
import std.algorithm, std.array, std.bigint, std.bitmanip, std.complex, std.container, std.math, std.mathspecial, std.numeric, std.regex, std.typecons;
import core.bitop;

class EOFException : Throwable { this() { super("EOF"); } }
string[] tokens;
string readToken() { for (; tokens.empty; ) { if (stdin.eof) { throw new EOFException; } tokens = readln.split; } auto token = tokens.front; tokens.popFront; return token; }
int readInt() { return readToken.to!int; }
long readLong() { return readToken.to!long; }
real readReal() { return readToken.to!real; }

bool chmin(T)(ref T t, in T f) { if (t > f) { t = f; return true; } else { return false; } }
bool chmax(T)(ref T t, in T f) { if (t < f) { t = f; return true; } else { return false; } }

int binarySearch(alias pred, T)(in T[] as) { int lo = -1, hi = cast(int)(as.length); for (; lo + 1 < hi; ) { const mid = (lo + hi) >> 1; (unaryFun!pred(as[mid]) ? hi : lo) = mid; } return hi; }
int lowerBound(T)(in T[] as, T val) { return as.binarySearch!(a => (a >= val)); }
int upperBound(T)(in T[] as, T val) { return as.binarySearch!(a => (a > val)); }


struct ModInt(int M_) {
  import std.conv : to;
  alias M = M_;
  int x;
  this(ModInt a) { x = a.x; }
  this(long a) { x = cast(int)(a % M); if (x < 0) x += M; }
  ref ModInt opAssign(long a) { return (this = ModInt(a)); }
  ref ModInt opOpAssign(string op)(ModInt a) {
    static if (op == "+") { x += a.x; if (x >= M) x -= M; }
    else static if (op == "-") { x -= a.x; if (x < 0) x += M; }
    else static if (op == "*") { x = cast(int)((cast(long)(x) * a.x) % M); }
    else static if (op == "/") { this *= a.inv(); }
    else static assert(false);
    return this;
  }
  ref ModInt opOpAssign(string op)(long a) {
    static if (op == "^^") {
      if (a < 0) return (this = inv()^^(-a));
      ModInt t2 = this, te = ModInt(1);
      for (long e = a; e > 0; e >>= 1) {
        if (e & 1) te *= t2;
        t2 *= t2;
      }
      x = cast(int)(te.x);
      return this;
    } else return mixin("this " ~ op ~ "= ModInt(a)");
  }
  ModInt inv() const {
    int a = x, b = M, y = 1, z = 0, t;
    for (; ; ) {
      t = a / b; a -= t * b;
      if (a == 0) {
        assert(b == 1 || b == -1);
        return ModInt(b * z);
      }
      y -= t * z;
      t = b / a; b -= t * a;
      if (b == 0) {
        assert(a == 1 || a == -1);
        return ModInt(a * y);
      }
      z -= t * y;
    }
  }
  ModInt opUnary(string op: "-")() const { return ModInt(-x); }
  ModInt opBinary(string op, T)(T a) const {
    return mixin("ModInt(this) " ~ op ~ "= a");
  }
  ModInt opBinaryRight(string op)(long a) const {
    return mixin("ModInt(a) " ~ op ~ "= this");
  }
  bool opCast(T: bool)() const { return (x != 0); }
  string toString() const { return x.to!string; }
}

enum MO = 1000000007;
alias Mint = ModInt!MO;


enum LIM = 2 * 10^^5 + 10;
Mint[] inv, fac, invFac;
void prepare() {
  inv = new Mint[LIM];
  fac = new Mint[LIM];
  invFac = new Mint[LIM];
  inv[1] = 1;
  foreach (i; 2 .. LIM) {
    inv[i] = -(Mint.M / i) * inv[cast(size_t)(Mint.M % i)];
  }
  fac[0] = invFac[0] = 1;
  foreach (i; 1 .. LIM) {
    fac[i] = fac[i - 1] * i;
    invFac[i] = invFac[i - 1] * inv[i];
  }
}
Mint binom(long n, long k) {
  if (0 <= k && k <= n) {
    assert(n < LIM);
    return fac[cast(size_t)(n)] * invFac[cast(size_t)(k)] * invFac[cast(size_t)(n - k)];
  } else {
    return Mint(0);
  }
}


Mint calc(int n, int k) {
  return Mint(n - k + 1) * Mint(n + 1)^^(k - 1);
}

void main() {
  prepare;
  
  /*
  debug {
    foreach (n; 1 .. 7 + 1) foreach (k; 1 .. n + 1) {
      int cnt;
      foreach (p; 0 .. n^^k) {
        auto freq = new int[n];
        foreach (i; 0 .. k) {
          ++freq[p / n^^i % n];
        }
        foreach_reverse (j; 0 .. n - 1) {
          freq[j] += freq[j + 1];
        }
        bool ok = true;
        foreach (j; 0 .. n) {
          ok = ok && (freq[j] <= n - j);
        }
        if (ok) {
          ++cnt;
          if (n <= 4) {
            writeln(iota(n).map!(i => (p / n^^i % n)));
          }
        }
      }
      writeln(n, " ", k, ": ", cnt);
      assert(cnt == (n - k + 1) * (n + 1)^^(k - 1));
    }
  }
  //*/
  
  try {
    for (; ; ) {
      const N = readInt();
      const M = readInt();
      const S = readToken();
      
      alias Query = Tuple!(string, "s", int, "sig");
      auto qss = new Query[][](M + 1);
      void pie(string s, int sig) {
        if (s.length >= 1 && s[0] == '-') {
          pie(s[1 .. $], sig);
          pie('o' ~ s[1 .. $], -sig);
        } else if (s.length >= 1 && s[$ - 1] == '-') {
          pie(s[0 .. $ - 1], sig);
          pie(s[0 .. $ - 1] ~ 'o', -sig);
        } else {
          qss[s.length] ~= Query(s, sig);
        }
      }
      pie(S, +1);
      debug {
        foreach (m; 0 .. M + 1) {
          writefln("qss[%s] = %s", m, qss[m]);
        }
      }
      
      Mint ans;
      
      // m = 0
      {
        int sigSum;
        foreach (ref q; qss[0]) {
          sigSum += q.sig;
        }
        ans += sigSum * Mint(N)^^N * Mint(N + 1);
      }
      
      foreach (m; 1 .. M + 1) {
        auto nums = new Mint[m + 1];
        foreach (ref q; qss[m]) {
          int insideSum;
          Mint insideNum = 1;
          for (int i = 0, j; i < m; i = j) {
            for (j = i; j < m && q.s[i] == q.s[j]; ++j) {}
            if (q.s[i] == '-') {
              insideSum += (j - i);
              insideNum *= calc(j - i, j - i) * invFac[j - i];
            }
          }
          nums[insideSum] += q.sig * insideNum;
        }
        debug {
          writefln("m = %s, nums = %s", m, nums);
        }
        
        /*
          0 <= k <= m
          calc(N - m, k) / k! * (k + insideSum)! * N^(N - (k + insideSum))
        */
        foreach (l; 0 .. m + 1) {
          if (nums[l]) {
            Mint sum;
            foreach (k; 0 .. N - m + 1) {
              sum += calc(N - m, k) * invFac[k] * fac[k + l] * Mint(N)^^(N - (k + l));
            }
            ans += nums[l] * sum;
          }
        }
      }
      
      ans *= (N - M + 1);
      writeln(ans);
    }
  } catch (EOFException e) {
  }
}