Removing Digits - C++

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

typedef long long ll;typedef long double llf;typedef double fl;typedef string str;typedef pair<double, double> dd;
typedef vector<int> vi;typedef vector<vector<int>> vvi;typedef vector<fl> vf;typedef vector<ll> vl;
typedef vector<llf> vlf;typedef vector<char> vc;typedef vector<str> vs;typedef pair<int,int> ii;
# define f(i,a,b,c) for(ll i=a;i<b;i+=c)
# define fd(i,a,b,c) for(ll i=a;i>=b;i-=c)
# define w(x) while(x--)
# define ctoi(a) (a-'0')
# define pb push_back
# define eb emplace_back
# define lb lower_bound
# define ub upper_bound
# define be(x) x.begin(), x.end()
# define rbe(x) x.rbegin(), x.rend()
# define _(x) ios::sync_with_stdio(0);cin.tie(0);cout.precision(x);cout.setf(ios::fixed);

int n, re=0;
int ma(int x){
    int mai, num;
    str p = to_string(x);
    mai=0;
    for(char i:p)num = ctoi(i), mai = max(mai, num);
    return mai;
}
int dp(int x){
    if(x==0)return re;
    ++re;
    return dp(x - ma(x));
}
int main(){_(0)
    cin>>n;
    cout<<dp(n)<<'\n';
return 0;}