import math

def is_perfect_square(n):
    """Check if a number is a perfect square."""
    root = int(math.sqrt(n))
    return root * root == n

def continued_fraction_sqrt(n):
    """Compute the continued fraction representation of sqrt(n)."""
    m, d, a = 0, 1, int(math.sqrt(n))
    initial_a = a
    period = []
    
    if initial_a * initial_a == n:  # Perfect square check
        return None, []
    
    while True:
        m = d * a - m
        d = (n - m * m) // d
        a = (initial_a + m) // d
        period.append(a)
        if a == 2 * initial_a:  # Period repeats here
            break
    
    return initial_a, period

def solve_pell_equation(n):
    """Solve Pell's equation x^2 - n * y^2 = 1 for the minimal solution."""
    if is_perfect_square(n):
        raise ValueError(f"The given number {n} is a perfect square, no solution exists.")
    
    a0, period = continued_fraction_sqrt(n)
    if not period:
        return None
    
    # Compute convergents using the periodic continued fraction
    p_prev, p_curr = 1, a0
    q_prev, q_curr = 0, 1
    
    for k in range(1, len(period) * 2 + 1):  # Repeat until period length is hit
        a_k = period[(k - 1) % len(period)]
        p_next = a_k * p_curr + p_prev
        q_next = a_k * q_curr + q_prev
        
        # Check if the solution satisfies Pell's equation
        if p_next * p_next - n * q_next * q_next == 1:
            return p_next, q_next
        
        # Update for the next iteration
        p_prev, p_curr = p_curr, p_next
        q_prev, q_curr = q_curr, q_next

if __name__ == '__main__':
    N = int(input())
    max_x = 0
    index = 2
    for i in range(2, N + 1):
        try:
            x, y = solve_pell_equation(i)
            if x > max_x:
                max_x = x
                index = i
        except ValueError as e:
            pass
    print(index)