import std.conv, std.functional, std.range, std.stdio, std.string;
import std.algorithm, std.array, std.bigint, std.complex, std.container, std.math, std.numeric, std.regex, std.typecons;
import core.bitop;

class EOFException : Throwable { this() { super("EOF"); } }
string[] tokens;
string readToken() { for (; tokens.empty; ) { if (stdin.eof) { throw new EOFException; } tokens = readln.split; } auto token = tokens.front; tokens.popFront; return token; }
int readInt() { return readToken.to!int; }
long readLong() { return readToken.to!long; }
real readReal() { return readToken.to!real; }

bool chmin(T)(ref T t, in T f) { if (t > f) { t = f; return true; } else { return false; } }
bool chmax(T)(ref T t, in T f) { if (t < f) { t = f; return true; } else { return false; } }

int binarySearch(alias pred, T)(in T[] as) { int lo = -1, hi = cast(int)(as.length); for (; lo + 1 < hi; ) { const mid = (lo + hi) >> 1; (unaryFun!pred(as[mid]) ? hi : lo) = mid; } return hi; }
int lowerBound(T)(in T[] as, T val) { return as.binarySearch!(a => (a >= val)); }
int upperBound(T)(in T[] as, T val) { return as.binarySearch!(a => (a > val)); }


enum INF = 10^^9;

void main() {
  try {
    for (; ; ) {
      const N = readInt();
      const S = readToken();
      
      /*
        3
        7
        11
        19
        59
        991
        9551
        555555555551
      */
      enum V = 2 * 2 * 2 * 3 * 4 * 12;
      auto dp = new int[][](2, V);
      dp[0][] = -INF;
      dp[1][] = -INF;
      dp[0][0] = 0;
      foreach (i; 0 .. N) {
        auto ch(int u, int v, int c) {
          chmax(dp[(i & 1) ^ 1][v], dp[i & 1][u] + c);
        }
        switch (S[i]) {
          case '3':
          case '7': {
            foreach (u; 0 .. V) {
              ch(u, u, 1);
            }
          } break;
          case '1': {
            foreach (u; 0 .. V) {
              ch(u, u, 0);
              if (u % 2 == 0) ch(u, u + 1, 0);
              if (u % 2 == 1) ch(u, u - 1, 1);
              if (u / 2 % 2 == 0) ch(u, u + 2, 0);
              if (u / 2 / 2 / 2 % 3 == 2) ch(u, u - 2 * 2 * 2 * 2, 1);
              if (u / 2 / 2 / 2 / 3 % 4 == 3) ch(u, u - 2 * 2 * 2 * 3 * 3, 1);
              if (u / 2 / 2 / 2 / 3 / 4 % 12 == 11) ch(u, u - 2 * 2 * 2 * 3 * 4 * 11, 1);
            }
          } break;
          case '5': {
            foreach (u; 0 .. V) {
              ch(u, u, 0);
              if (u / 2 / 2 % 2 == 1) ch(u, u - 2 * 2, 1);
              if (u / 2 / 2 / 2 / 3 % 4 == 1) ch(u, u + 2 * 2 * 2 * 3, 0);
              if (u / 2 / 2 / 2 / 3 % 4 == 2) ch(u, u + 2 * 2 * 2 * 3, 0);
              if (u / 2 / 2 / 2 / 3 / 4 % 12 != 11) ch(u, u + 2 * 2 * 2 * 3 * 4, 0);
            }
          } break;
          case '9': {
            foreach (u; 0 .. V) {
              ch(u, u, 0);
              if (u / 2 % 2 == 1) ch(u, u - 2, 1);
              if (u / 2 / 2 % 2 == 1) ch(u, u - 2 * 2, 1);
              if (u / 2 / 2 / 2 % 3 == 0) ch(u, u + 2 * 2 * 2, 0);
              if (u / 2 / 2 / 2 % 3 == 1) ch(u, u + 2 * 2 * 2, 0);
              if (u / 2 / 2 / 2 / 3 % 4 == 0) ch(u, u + 2 * 2 * 2 * 3, 0);
            }
          } break;
          default: assert(false);
        }
      }
      
      const ans = dp[N & 1].maxElement;
      writeln(ans);
    }
  } catch (EOFException e) {
  }
}