#include <stdio.h>
int maxdigit(int n){
int arr[20];
int j=0;
while(n!=0){
int y=n%10;
arr[j]=y;
j++;
n=n/10;
}
int max=arr[0];
for(int i=0;i<n;i++){
if(max<arr[i]){
max=arr[i];
}
}
return max;
}
int main(){
int n;
scanf("%d",&n);
int x=maxdigit(n);
printf("%d",x);
}
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