#include <bits/stdc++.h>
using namespace std;
const int N = 1000;
const double eps = 1e-9;
long long INF = 1e9;
const int OO = 0x3f3f3f3f;
int dx[] = {1, -1, 0, 0, 1, -1, 1, -1};
int dy[] = {0, 0, 1, -1, 1, -1, -1, 1};
bool comp(pair<int, int> a, pair<int, int> b) {
  if (a.first < b.first)
    return true;
  else if (a.first > b.first)
    return false;
  else
    return a.first < b.first;
}
void read(string str, int node) {
  stringstream ss;
  int number;
  ss << str;
  while (ss >> number) cout << number << endl;
}
long long fp(long long b, long long p) {
  if (p == 0) return 1;
  if (p % 2 == 0) return fp((b * b) % INF, p / 2);
  return (fp(b, p - 1) * b) % INF;
}
unsigned long long read_binary(string s) {
  unsigned long long x = 0, tmp = 1;
  for (int i = s.size() - 1; i >= 0; i--) {
    x = (x + tmp * (s[i] - '0')) % INF;
    tmp = (tmp * 2) % INF;
  }
  return x;
}
long long com(long long x, long long y) {
  long long sum = 1;
  for (int i = 1; i <= y; i++) {
    sum *= x;
    x--;
    sum /= i;
  }
  return sum;
}
long long gcd(long long n1, long long n2) {
  if (n2 != 0)
    return gcd(n2, n1 % n2);
  else
    return n1;
}
int setBit(int num, int idx, int val = 1) {
  return (val) ? (num | (1 << idx)) : (num & ~(1 << idx));
}
int getBit(int num, int idx) { return ((num >> idx) & 1) == 1; }
int cntBit(int num) {
  int ret = 0;
  while (num) {
    if (num % 2) ret++;
    num /= 2;
  }
  return ret;
}
bool sum[1500];
void sieve() {
  sum[0] = sum[1] = 1;
  for (int i = 2; i * i < 1002; i++) {
    if (!sum[i]) {
      for (int j = 2 * i; j < 1002; j += i) {
        sum[j] = 1;
      }
    }
  }
}
int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  ;
  long long n;
  cin >> n;
  string s = to_string(n);
  long long mi = INF;
  for (int i = 0; i < (1 << s.size()); ++i) {
    int cnt = 0;
    string k;
    for (int j = 0; j < s.size(); j++) {
      if (i & (1 << j)) {
        k += s[j];
        cnt++;
      }
    }
    if (k[0] == '0') continue;
    long long val;
    istringstream ss(k);
    ss >> val;
    double d = sqrt(val);
    int ii = sqrt(val);
    if (d == ii) {
      mi = min(mi, (long long)s.size() - cnt);
    }
  }
  if (mi == INF)
    cout << -1 << endl;
  else
    cout << mi << endl;
}
