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;
}