https://www.pbinfo.ro/probleme/2288/cifraimparamaxima

#include <iostream>
using namespace std;

int main(){
    int n;
    cin >> n;
    int cmax= -1;
    while(n){
        if(n % 2 == 1)
            if(n%10>cmax)
                cmax = n%10;
        n /= 10;
    }
    if(cmax == -1)
        cout << "nu exista";
    else
        cout << cmax << endl;

    return 0;
}