简单的容斥原理
要注意int会溢出
#include<iostream>
#include<cstdio>
#include<cstring>
#include<algorithm>
#include<cmath>
using namespace std;
typedef long long ll;
const int N=20;
ll a[N];
ll gcd(ll a,ll b){return b==0?a:gcd(b,a%b);}
ll lcm(ll a,ll b){return a*b/gcd(a,b);}
int main()
{
ll n,m;
while(~scanf("%lld%lld",&n,&m))
{
for(ll i=0;i<m;i++)
scanf("%lld",&a[i]);
ll end=(1<<m);
ll sum=0;
for(ll i=1;i<end;i++)
{
ll tmp=1,num=0;
for(ll j=0;j<m;j++)
{
if((1<<j)&i) tmp=lcm(tmp,a[j]),num++;
if(tmp>n) break;
}
if(num%2==1) sum+=n/tmp;
else sum-=n/tmp;
}
printf("%lld\n",n-sum);
}
return 0;
}