#include <bits/stdc++.h>
using namespace std;
int fx[] = {1, -1, 0, 0};
int fy[] = {0, 0, 1, -1};
int n;
int ara[120][120], orig[120][120];
long long dp[27];
int main() {
  std::ios_base::sync_with_stdio(false);
  int n, k;
  cin >> n >> k;
  string str;
  cin >> str;
  for (int i = 0; i <= (int)str.size() - 1; i++) {
    long long sum = 0;
    for (int j = 0; j <= k - 1; j++) {
      sum = (sum + dp[j]) % 1000000007;
    }
    dp[str[i] - 'a'] = (sum + 1LL) % 1000000007;
  }
  stack<int> stk;
  bool vis[27];
  memset(vis, 0, sizeof(vis));
  for (int i = (int)str.size() - 1; i >= 0; i--) {
    if (vis[str[i] - 'a'] == 0) {
      vis[str[i] - 'a'] = 1;
      stk.push(str[i] - 'a');
    }
  }
  for (int i = 0; i <= k - 1; i++) {
    if (vis[i] == 0) {
      stk.push(i);
    }
  }
  queue<int> q;
  while (!stk.empty()) {
    q.push(stk.top());
    stk.pop();
  }
  for (int i = 1; i <= n; i++) {
    int top = q.front();
    q.pop();
    long long sum = 0;
    for (int j = 0; j <= k - 1; j++) {
      sum = (sum + dp[j]) % 1000000007;
    }
    dp[top] = (sum + 1LL) % 1000000007;
    q.push(top);
  }
  long long ans = 0;
  for (int i = 0; i <= k - 1; i++) {
    ans = (ans + dp[i]) % 1000000007;
  }
  cout << (ans + 1) % 1000000007;
  return 0;
}
