codeforces - 110 - C (py)

C.py

#!/usr/bin/env python2.6
"""(c) gorlum0 [at] gmail.com"""
from sys import stdin
MAXN = 10**6

dp = [0] * (MAXN+1)
dp[0] = 1

for i in xrange(MAXN+1):
    if dp[i-7]:
        dp[i] = 7
    elif dp[i-4]:
        dp[i] = 4

for n in map(int, stdin):
    if not dp[n]:
        print -1; continue

    lucky = []
    while n:
        lucky.append(dp[n])
        n -= dp[n]
    lucky.reverse()
    print ''.join(map(str, lucky))