#include<iostream>
using namespace std;
 
long long max(long long a, long long b) {
    return a > b ? a : b;
}
 
int main() {
    long long n, m;
    cin >> n >> m;
    long long res = 0;
    if(n % 3 && m % 3 == 0) {
        cout << -1;
        return 0;
    }
    else {
        long long MAX = max(3, m), MIN = 3 * m / MAX;
        long long tmp = n / MAX;
        while(tmp >= 0) {
            if((n - tmp * MAX) % MIN == 0) {
                res = tmp + (n - tmp * MAX) / MIN;
                break;
            }
            tmp--;
        }
    }
    if(res == 0) cout << -1;
    else cout << res;
}

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