import numpy as np

N, P = map(int, input().split())
abc = [[int(_) for _ in input().split()] for _ in range(N)]
dp = np.zeros([N+1, P+3], dtype=int)

for i in range(1, N+1):
    dp[i][0] = dp[i-1][0] + abc[i-1][0]
    dp[i][1] = min(dp[i-1][1] + abc[i-1][0], dp[i-1][0] + abc[i-1][1])
    dp[i][2] = min(dp[i-1][2]+abc[i-1][0], dp[i-1][1]+abc[i-1][1], dp[i-1][0]+abc[i-1][2])
    dp[i][3:] = np.minimum(np.minimum(np.minimum(dp[i-1][:-3]+1, dp[i-1][1:-2]+abc[i-1][2]), dp[i-1][2:-1]+abc[i-1][1]), dp[i-1][3:]+abc[i-1][0])

print(dp[N][P]/N)