C :

#include<stdio.h>
int main()
{
    int x,a,b,c,d,max=0;
    scanf("%d",&x);
    a=x/1000;
    b=x/100%10;
    c=x/10%10;
    d=x%10;
if(a>max)
    max=a;
    if(b>max)
        max=b;
    if(c>max)
        max=c;
    if(d>max)
        max=d;
    printf("%d",max);
    return 0;
}

C++ :

#include <bits/stdc++.h>
using namespace std;

int main() {
	int a[4],n;
	cin>>n;
	a[0] = n / 1000;
	a[1] = n / 100 % 10;
	a[2] = n / 10 % 10;
	a[3] = n % 10;
	
	sort(a,a+4);
	
	cout<<a[3];
}

Java :

import java.util.Scanner;
public class Main
{   
	public static void main(String[] args){
        Scanner sc = new Scanner(System.in);
        int x = sc.nextInt();
        int a = x/1000;
        int b = x/100%10;
        int c = x/10%10;
        int d = x%10;
        int max =a;
        if(max<b) {
        	max = b;
        }
        if(max<c) {
        	max = c;
        }
        if(max<d) {
        	max = d;
        }
        System.out.println(max);
    }
}

Python :

n = int(input())
q = n // 1000 % 10
b = n // 100 % 10
s = n // 10 % 10
g = n // 1 % 10
mx = max(g, s, b, q)
print(mx)