import sys

def main():
    input = sys.stdin.read().split()
    N = int(input[0])
    M = int(input[1])
    P = int(input[2])
    A = list(map(int, input[3:3+N]))
    
    min_steps = float('inf')
    
    for a in A:
        ai = a
        a_i = 0
        while ai % P == 0:
            a_i += 1
            ai = ai // P
        b_i = ai
        
        product = (P ** a_i) * b_i
        
        if product > M:
            min_steps = min(min_steps, 1)
            continue
        
        if b_i == 1:
            continue
        
        required = M // product
        k = 0
        current = 1
        while current <= required:
            current *= b_i
            k += 1
        
        steps_i = k * (1 + a_i)
        candidate = steps_i + 1
        min_steps = min(min_steps, candidate)
    
    if min_steps == float('inf'):
        print(-1)
    else:
        print(min_steps)

if __name__ == "__main__":
    main()