#include <bits/stdc++.h>
using namespace std;
 
int main() {
  int A;
  cin >> A;
  int B;
  cin >> B;
  int W;
  cin >> W;
  int i = 0;
  int a = 0;
  int c, d;
  int w = W * 1000;
  while (true) {
    i++;
    if (a == 0) {
      if (A * i <= w && B * i >= w) {
        a = 1;
        c = i;
      }
    }
    else if (a == 1) {
      if (A * i > w) {
        a = 2;
        d = i - 1;
        break;
      }
    }
    if (a == 0 && i >= 1000000) {
      break;
    }
  }
  if (a == 2) {
    cout << c << " " << d << endl;
  }
  if (a == 0) {
    cout << "UNSATISFIABLE" << endl;
  }
}
#include <bits/stdc++.h>
using namespace std;
typedef long long ll;//三年竞赛一场空，不开long long见祖宗
//typedef __int128 lll;
#define print(i) cout << "debug: " << i << endl
#define close() ios::sync_with_stdio(0), cin.tie(0), cout.tie(0)
#define mem(a, b) memset(a, b, sizeof(a))
#define pb(a) push_back(a)
#define x first
#define y second
typedef pair<int, int> pii;
const ll mod = 1e9 + 7;
const int maxn = 4e5 + 10;
const int inf = 0x3f3f3f3f;
double a[maxn], b[maxn];
const double eps=1e-6;
int vis[maxn];
int n, m, k;

inline int sgn(double x)
{
	if(x>-eps && x<eps)
		return 0;
	if(x>0) return 1;
	else	return -1;
}

int main()
{
    cin >> n >> m >> k;
    for(int i = 1; i <= k; i++)
    {
        int x; cin >> x; vis[x] = 1;
    }
    double suma = 0, sumb = 0;
    for(int i = n - 1; i >= 0; i--)
    {
        if(vis[i])
        {
            a[i] = 1, b[i] = 0;
        }
        else
        {
            a[i] = suma / m, b[i] = sumb / m + 1;
        }
        suma += a[i], suma -= a[i + m];
        sumb += b[i], sumb -= b[i + m];
    }
    //cout << a[1] << " " << b[1] << endl;
    if(sgn(a[0] - 1) == 0) cout << -1 << endl;
    else
    {
        double res = b[0] / (1 - a[0]);
        printf("%.4f\n", res);
    }
    
}
