#include <bits/stdc++.h>
using namespace std;
inline long long gcd(long long a, long long b) {
  a = ((a) < 0 ? -(a) : (a));
  b = ((b) < 0 ? -(b) : (b));
  while (b) {
    a = a % b;
    swap(a, b);
  }
  return a;
}
long long ext_gcd(long long A, long long B, long long *X, long long *Y) {
  long long x2, y2, x1, y1, x, y, r2, r1, q, r;
  x2 = 1;
  y2 = 0;
  x1 = 0;
  y1 = 1;
  for (r2 = A, r1 = B; r1 != 0;
       r2 = r1, r1 = r, x2 = x1, y2 = y1, x1 = x, y1 = y) {
    q = r2 / r1;
    r = r2 % r1;
    x = x2 - (q * x1);
    y = y2 - (q * y1);
  }
  *X = x2;
  *Y = y2;
  return r2;
}
inline long long modInv(long long a, long long m) {
  long long x, y;
  ext_gcd(a, m, &x, &y);
  x %= m;
  if (x < 0) x += m;
  return x;
}
inline long long power(long long a, long long p) {
  long long res = 1, x = a;
  while (p) {
    if (p & 1) res = (res * x);
    x = (x * x);
    p >>= 1;
  }
  return res;
}
inline long long bigmod(long long a, long long p, long long m) {
  long long res = 1 % m, x = a % m;
  while (p) {
    if (p & 1) res = (res * x) % m;
    x = (x * x) % m;
    p >>= 1;
  }
  return res;
}
struct node {
  long long a, t, i;
  inline node() {}
  inline node(long long a, long long t) : a(a), t(t) {}
  inline bool operator<(const node &other) const { return a < other.a; }
};
char s[20];
int p[20];
int n, m;
long long tmp;
int ans;
bool fnd;
int main() {
  scanf("%s", s);
  n = strlen(s);
  ans = n;
  for (long long i = 1; i * i < 2011111111; i++) {
    m = 0;
    tmp = i * i;
    while (tmp) {
      p[m++] = tmp % 10;
      tmp /= 10;
    }
    if (m > n) break;
    int k = m - 1;
    for (int j = 0; k >= 0 && j < n; j++) {
      int cur = s[j] - '0';
      if (cur == p[k]) {
        k--;
      }
    }
    if (k == -1) {
      ans = min(ans, n - m);
      fnd = 1;
    }
  }
  if (!fnd) ans = -1;
  printf("%d", ans);
  return 0;
}
