# Enter your code here. Read input from STDIN. Print output to STDOUT
import math

def is_square(n):
    sqrt_n = int(math.sqrt(n))
    return sqrt_n * sqrt_n == n

def minimal_solution(D):
    m, d, a = 0, 1, int(math.sqrt(D))
    num1, num2 = 1, a
    den1, den2 = 0, 1

    while num2*num2 - D*den2*den2 != 1:
        m = d*a - m
        d = (D - m*m) // d
        a = (int(math.sqrt(D)) + m) // d

        num1, num2 = num2, a*num2 + num1
        den1, den2 = den2, a*den2 + den1

    return num2

def largest_minimal_solution(limit):
    max_D = 0
    max_minimal_solution = 0

    for D in range(2, limit + 1):
        if not is_square(D):
            solution = minimal_solution(D)
            if solution > max_minimal_solution:
                max_minimal_solution = solution
                max_D = D

    return max_D

# Read input and calculate the result
limit = int(input())
result = largest_minimal_solution(limit)
print(result)