#include<bits/stdc++.h>
using namespace std;
int zhishu[]={2,3,5,7,11,13,17,19,23,29,31,37,41,43,47,53,59,61,67,71,73,79,83,89,97};
int zimubiao[26] = {0};

int main(){
    string s;
    cin >> s;
    for(int i=0; i<s.length(); i++){
        zimubiao[s[i]-'a']++;
    }
    
    int maxn=0, minn=101;
    for(int i=0; i<26; i++){
        if(zimubiao[i] > maxn) maxn = zimubiao[i];
        if(zimubiao[i] < minn && zimubiao[i] > 0) minn = zimubiao[i];
    }
    
    int diff = maxn - minn;
    bool isLucky = false;
    for(int i=0; i<25; i++){
        if(diff == zhishu[i]){
            isLucky = true;
            break;
        }
    }
    
    if(isLucky){
        cout << diff << endl;
    }else{
        cout << 0 << endl;
    }
    return 0;
}

新手代码过于史山，勿骂