import collections
import math

def solve(N, L, R):
    if R < N:
        return 0
    if L > 6 * N:
        return 0
    if L < N and R > 6 * N:
        return 1
    if N < 100:
        return solve_exact(N, L, R)
    else:
        return solve_approximate(N, L, R)

def solve_exact(N, L, R):
    fs = {0: 1}
    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
        fs = nfs
    cum = 0
    for v, p in fs.items():
        if L <= v and v <= R:
            cum += p
    return cum/(6**N)


def solve_approximate(N, L, R):
    E = N * 3.5
#    Var = N * 35/12
    if R >= N * 6:
        pR = 0.5
    elif R < N:
        pR = -0.5
    else:
        pR = math.erf((2*R + 1 - N * 7)/math.sqrt(N*70/3)) / 2
    if L >= N * 6:
        pL = 0.5
    elif L < N:
        pL = -0.5
    else:       
        pL = math.erf((2*L - 1 - N * 7)/math.sqrt(N*70/3)) / 2
    return pR - pL
                

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('{:f}'.format(solve(N, L, R)))