#include <bits/stdc++.h>
const int TABLE_LENGTH = 100001;
double table[TABLE_LENGTH] = {0};
int main() {
  int k, n, m;
  double answer = 0.0;
  scanf("%d%d%d", &n, &m, &k);
  if (m <= k) {
    answer = 1.0;
  } else if (n + k < m) {
    answer = 0.0;
  } else {
    for (int i = 0; i < TABLE_LENGTH; i++) {
      table[i] = i + 1;
    }
    for (int i = 0; i < k; i++) {
      for (int j = 0; j < TABLE_LENGTH; j++) {
        table[j] += table[j - 1];
      }
    }
    answer = 1.0 - table[m - k - 1] / table[n];
  }
  printf("%lf\n", answer);
  return 0;
}
