#include<bits/stdc++.h>
using namespace std;
string n;
int minn=1e9;
inline void dfs(int id,int s,int num){
    if(num>=minn)return;
    if(id>n.length())return;
    if(id==(signed int)n.length()&&sqrt(s)==(int)sqrt(s)&&num!=n.length()){
        minn=num;
        return;
    }
    dfs(id+1,s*10+(n[id]-'0'),num);
    dfs(id+1,s,num+1);
}
int main(){
    cin>>n;
    dfs(0,0,0);
    cout<<(minn==1e9?-1:minn)<<endl;
    return 0;
}