題目連結：https://www.luogu.org/problemnew/show/SP6285

唉好久之前校內模擬賽的題目

嘴上說著明白但是實現起來我的位運算太醜陋了啊！

#include <cstdio>
#include <cstring>
#include <iostream>
#include <algorithm>
#define ll long long
using namespace std;
const int maxn = 300;
ll n, k, a[maxn], ans;
ll gcd(ll x, ll y)
{
    if(x % y == 0) return y;
    else return gcd(y, x%y);
}
ll lcm(ll x, ll y)
{
    return x / gcd(x,y) * y;
}
int main()
{
    ios::sync_with_stdio(false);
    cin>>n>>k;
    for(ll i = 0; i < k; i++) cin>>a[i];
    for(ll i = 1; i < (1 << k); i++)
    {
        ll res = 1, flag = 0;
        for(ll j = 0; j < k; j++)
        {
            if(i & (1 << j)) 
            { 
                res = lcm(res, a[j]);
                flag++;
            }
        }
        if(flag & 1) ans += (n/res);
        else ans -= (n/res);
    }
    cout<<n-ans;
    return 0;
}