2853: 小A的游戏昵称

http://acm.zzuli.edu.cn/problem.php?id=2853

数学问题：容斥定理

#include<iostream>
#include<algorithm>
using namespace std;
int main()
{
    
    
	long long n;
	long long a,b,c,d,e,f,g,sa,sb,sc,sd,se,sf,sg;
	
	cin>>n;
	a=n/3;
	sa=3*a*(1+a)/2;
	
	b=n/5;
	sb=5*b*(1+b)/2;

	c=n/7;
	sc=7*c*(1+c)/2;

	d=n/105;
	sd=105*d*(1+d)/2;
	
	e=n/15;
	se=15*e*(1+e)/2;
	
	f=n/21;
	sf=21*f*(1+f)/2;
	
	g=n/35;
	sg=35*g*(1+g)/2;
	
	long long ans=sa+sb+sc+sd-se-sf-sg;
	printf("%lld\n",(ans+998244353)%998244353);
	return 0;
}