bạn tự đọc file nhé!

#include <bits/stdc++.h>
using namespace std;
signed main(){
	int n;
	cin>>n;
	int maxx=n%10;
	while(n){
		maxx=max(maxx,n%10);
		n/=10;
	}
	cout<<maxx;
}

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

int main(){
    freopen("BAI2.inp","r",stdin);
    freopen("BAI2.out","w",stdin);
    ll n,s=0;
    cin>>n;
    while (n>0){
        s=max(s,n%10);
        n/=10;
    }
    cout<<s;
    //meothinhle
    return 0;
}