import collections import math def solve(N, L, R): if N < 300: return solve_exact(N, L, R) else: return solve_approximate(N, L, R) def solve_exact(N, L, R): fs = {0: 1.0} for n in range(N-1, -1, -1): nfs = collections.defaultdict(float) for v, p in fs.items(): for dice in range(1, 7): nv = v + dice if nv + n <= R and nv + n * 6 >= L: nfs[nv] += p * 1/6 fs = nfs cum = 0.0 for v, p in fs.items(): if L <= v and v <= R: cum += p return cum def solve_approximate(N, L, R): E = N * 3.5 Var = N * 35.0/12.0 r = (R + 0.5 - E)/math.sqrt(Var) l = (L - 0.5 - E)/math.sqrt(Var) return phi(r) - phi(l) def phi(x): return (1.0 + math.erf(x / math.sqrt(2.0))) / 2.0 N = int(input()) L, R = map(int, input().split()) print(solve(N, L, R))