很简单，直接调用两次__gcd()就行了

#include <iostream>
#include <algorithm>
using namespace std;

int main(){
    int a, b, c;
    cin >> a >> b >> c;
    int ab = a * b / __gcd(a, b);
    int abc = ab * c / __gcd(ab, c);
    cout << abc;
    return 0;
}