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import java.io.*;
import java.util.*;
import java.math.*;

public class utkarsh {

    InputStream is;
    PrintWriter out;
    
    void solve(){
        //Enter code here utkarsh
        char[] c = ns().toCharArray();
        int n = c.length;
        ArrayList <Integer> a[] = new ArrayList[26];
        for(int i = 0; i < 26; i++) {
            a[i] = new ArrayList<>();
        }
        for(int i = 0; i < n; i++) {
            a[c[i] - 'a'].add(i);
        }
        int b[] = new int[26];
        int x = 0;
        int y, z;
        for(int i = 0; i < 26; i++) {
            if(a[i].isEmpty())  continue;
            if(a[i].size() == 1) {
                x++;
                continue;
            }
            z = 0;
            for(int j = 1; j < n; j++) {
                Arrays.fill(b, 0);
                for(int u : a[i]) {
                    int k = (u + j) % n;
                    k = c[k] - 'a';
                    b[k]++;
                }
                y = 0;
                for(int k = 0; k < 26; k++) {
                    if(b[k] == 1) {
                        y++;
                    }
                }
                if(y > z)   z = y;
            }
            x += z;
        }
        out.println((x + 0.0) / (n + 0.0));
    }
    
    public static void main(String[] args) { new utkarsh().run();
    }
    void run(){ is = System.in; out = new PrintWriter(System.out); solve(); out.flush();
    }
    
    byte input[] = new byte[1024];
    int len = 0, ptr = 0;
    
    int readByte(){ if(ptr >= len){ ptr = 0; try{ len = is.read(input); }catch(IOException e){ throw new InputMismatchException(); } if(len <= 0){ return -1; } } return input[ptr++];
    }
    boolean isSpaceChar(int c){ return !( c >= 33 && c <= 126 ); 
    }
    int skip(){ int b = readByte(); while(b != -1 && isSpaceChar(b)){ b = readByte(); } return b;
    }
    
    char nc(){ return (char)skip();
    }
    String ns(){ int b = skip(); StringBuilder sb = new StringBuilder(); while(!isSpaceChar(b)){ sb.appendCodePoint(b); b=readByte(); } return sb.toString();
    }
    int ni(){ int n = 0,b = readByte(); boolean minus = false; while(b != -1 && !( (b >= '0' && b <= '9') || b == '-')){ b = readByte(); } if(b == '-'){ minus = true; b = readByte(); } if(b == -1){ return -1; } while(b >= '0' && b <= '9'){ n = n * 10 + (b - '0'); b = readByte(); } return minus ? -n : n;
    }
    long nl(){ long n = 0L; int b = readByte(); boolean minus = false; while(b != -1 && !( (b >= '0' && b <= '9') || b == '-')){ b = readByte(); } if(b == '-'){ minus = true; b = readByte(); } while(b >= '0' && b <= '9'){ n = n * 10 + (b - '0'); b = readByte(); } return minus ? -n : n;
    }
    double nd(){ return Double.parseDouble(ns());
    }
    float nf(){ return Float.parseFloat(ns());
    }
    int[] na(int n){ int a[] = new int[n]; for(int i = 0; i < n; i++){ a[i] = ni(); } return a;
    }
    char[] ns(int n){ char c[] = new char[n]; int i,b = skip(); for(i = 0; i < n; i++){ if(isSpaceChar(b)){ break; } c[i] = (char)b; b = readByte(); } return i == n ? c : Arrays.copyOf(c,i);
    }
}