#include <bits/stdc++.h>
#define REP(i, a, n) for(ll i = ((ll) a); i < ((ll) n); i++)
#define EPS 1e-10
using namespace std;
typedef long long ll;

ll F, N, K;
double dp[20][101][101][101];

int main(void) {
  cin >> F >> N >> K;

  REP(f, 0, F) REP(i, 0, 101) REP(j, 0, 101) REP(k, 0, 101) dp[f][i][j][k] = 0;
  REP(f, 0, F) dp[f][0][0][0] = 1;

  REP(f, 0, F) {
    REP(i, 0, N) REP(j, 0, N) REP(k, 0, N) if(dp[f][i][j][k] > EPS) {
      REP(g, 0, F) {
        if(g >  f) dp[f][i + 1][j + 1][k] += dp[f][i][j][k];
        if(g == f) dp[f][i + 1][j][k + 1] += dp[f][i][j][k];
        if(g <  f) dp[f][i + 1][j][k] += dp[f][i][j][k];
      }
    }
  }

  double p = 1;
  REP(i, 0, N) p /= F;

  double ans = 0;
  REP(f, 0, F) {
    REP(j, 0, N + 1) REP(k, 0, N + 1) {
      if(j < K && K <= j + k) ans += (f + 1) * dp[f][N][j][k] * p;
    }
  }
  printf("%.15lf\n", ans);
}