C++ :

#include<bits/stdc++.h>
using namespace std;
int main()
{
	int a;
	cin>>a;
	if(a<10) cout<<"1";
	else if(a<100) cout<<"2";
	else if(a<1000) cout<<"3";
	else cout<<"4";
	return 0;
}

Java :

import java.util.Scanner;

public class Main {

	public static void main(String[] args) {
		// TODO Auto-generated method stub
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		int g = n % 10;
		int s = n / 10 % 10;
		int b = n / 100 % 10;
		int q = n / 1000;
		if(q > 0){
			System.out.println(4);
		}if(q == 0 && b > 0){
			System.out.println(3);
		}if(q == 0 && b == 0 && s > 0){
			System.out.println(2);
		}if(q == 0 && b == 0 && s == 0 && g > 0){
			System.out.println(1);
		}if(n == 0){
			System.out.println(0);
		}
		sc.close();
	}

}