import java.io.BufferedReader;
import java.io.InputStreamReader;

class Main
{
	public static void main (String[] args) throws java.lang.Exception
	{
		BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(System.in));
		String p = bufferedReader.readLine();
		long s=0;
		long[] x= {0,0,0,0,0,0,0,0,0,0};
		for(int i = 0; i < p.length(); i++) {
			char n = p.charAt(i);
			if(n =='0') x[0]++;
			else if(n =='1') x[1]++;
			else if(n =='2') x[2]++;
			else if(n =='3') x[3]++;
			else if(n =='4') x[4]++;
			else if(n =='5') x[5]++;
			else if(n =='6') x[6]++;
			else if(n =='7') x[7]++;
			else if(n =='8') x[8]++;
			else if(n =='9') x[9]++;
		}
		for(int i = 0; i < 10; i++)
			if (x[i]>1) s+=x[i]/2;
		System.out.print(s);
	}
}