#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;
}

/**************************************************************
	Problem: 1718
	User: admin
	Language: C
	Result: Accepted
	Time:37 ms
	Memory:1144 kb
****************************************************************/