#68 CifraMaxima

#include <iostream>
using namespace std;

int main()
{
    int n;
    cin >> n;
    int cmax= n%10;

    while(n)
    {

        if(n%10>cmax)
            cmax = n%10;
        n /= 10;
    }

    cout << cmax << endl;

    return 0;
}