def inp() a=gets.chomp.split(" ").map(&:to_i)end 
def inpf() a=gets.chomp.split(" ").map(&:to_f)end
def inps() a=gets.chomp.split(" ")end  
def copy(a) Marshal.load(Marshal.dump(a)) end
def kaizyo(n)(n < 2)? 1 : (2..n).inject(:*) end
def scount(a,b) a.each{|n|b[n]+=1} end
def na(n,d=0) Array.new(n,d)end
def na2(n,m,d=0) Array.new(n){Array.new(m,d)}end
def na3(n,m,l,d=0) Array.new(n){Array.new(m){Array.new(l,d)}}end
sosu = "2,3,5,7,11,13,17,19,23,29,31,37,41,43,47,53,59,61,67,71,73,79,83,89,97,101,
103,107,109,113,127,131,137,139,149,151,157,163,167,173,179,181,191,193,197,
199,211,223,227,229,233,239,241,251,257,263,269,271,277,281,283,293,307,311,
313,317,331,337,347,349,353,359,367,373,379,383,389,397,401,409,419,421,431,
433,439,443,449,457,461,463,467,479,487,491,499,503,509,521,523,541,547,557,
563,569,571,577,587,593,599,601,607,613,617,619,631,641,643,647,653,659,661,
673,677,683,691,701,709,719,727,733,739,743,751,757,761,769,773,787,797,809,
811,821,823,827,829,839,853,857,859,863,877,881,883,887,907,911,919,929,937,
941,947,953,967,971,977,983,991,997,1009,1013,1019,1021,1031,1033,1039,1049,
1051,1061,1063,1069,1087,1091,1093,1097,1103,1109,1117,1123,1129,1151,1153,
1163,1171,1181,1187,1193,1201,1213,1217,1223,1229,1231,1237,1249,1259,1277,
1279,1283,1289,1291,1297,1301,1303,1307,1319,1321,1327,1361,1367,1373,1381,
1399,1409,1423,1427,1429,1433,1439,1447,1451,1453,1459,1471,1481,1483,1487,
1489,1493,1499,1511,1523,1531,1543,1549,1553,1559,1567,1571,1579,1583,1597,
1601,1607,1609,1613,1619,1621,1627,1637,1657,1663,1667,1669,1693,1697,1699,
1709,1721,1723,1733,1741,1747,1753,1759,1777,1783,1787,1789,1801,1811,1823,
1831,1847,1861,1867,1871,1873,1877,1879,1889,1901,1907,1913,1931,1933,1949,
1951,1973,1979,1987,1993,1997,1999"
sosu = sosu.delete("\n").split(",").map(&:to_i)
n = inp[0]
dp = na(n+1)
max = 0
sosu.reverse!
sosu.each_with_index do |d,i|
  dp[d] = 1
  ((d+1)..(n-d)).reverse_each do |m|
    [m,dp[m]]
    if(dp[m] != 0)
      if(dp[m+d]<dp[m]+1)
        dp[m+d] = dp[m]+1 if(m+d < 20001) 
      end
    end
  end
end
p (dp[n] == 0)? -1 : dp[n]