Removing Digits

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

#define int long long

int f(int n){
    if(!n)
        return 0;
    int m = 0;
    int x = n;
    while(n){
        m = max(m , n % 10);
        n /= 10;
    }
    return 1 + f(x - m);
}

signed main()
{
    int n;
    cin >> n;
    cout << f(n) << endl;
}