#include <cstdio>
#include <string>
#include <algorithm>
char buf [102];
int main() {
    scanf("%s", buf); std::string s = buf;
    printf("%d\n", s.length() > 1 && std::all_of(++s.begin(), s.end(), [](const char &c){ return c == '3'; }) ? int(s.length() - 1) : -1);
}