#include <algorithm>
#include <bitset>
#include <cassert>
#include <cctype>
#include <cmath>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <ctime>
#include <deque>
#include <functional>
#include <iomanip>
#include <iostream>
#include <list>
#include <map>
#include <numeric>
#include <queue>
#include <set>
#include <sstream>
#include <stack>
#include <string>
#include <utility>
#include <vector>

#define REP(i,s,n) for(int i=(int)(s);i<(int)(n);i++)

using namespace std;
typedef long long int ll;
typedef vector<int> VI;
typedef pair<int, int> PI;
const double EPS=1e-9;
const int LIM = 10000;


int main(void){
  ll n, l, r;
  cin >> n >> l >> r;
  if (n < LIM) {
    assert(0);
  } else {
    double lb = (l - 1.0 - 3.5 * n) / sqrt(35.0 / 6.0 * n);
    double rb = (r - 3.5 * n) / sqrt(35.0 / 6.0 * n);
    double res = 0.5 * (erf(rb) - erf(lb));
    printf("%.15f\n", res);
  }
}