萌新（你猜是不是妹子）求助嘤嘤嘤

/*(^-^)*/
#include<map>
#include<set>
#include<stack>
#include<queue>
#include<cmath>
#include<ctime>
#include<cstdio>
#include<vector>
#include<cctype>
#include<string>
#include<iomanip>
#include<cstdlib>
#include<cstring>
#include<iostream>
#include<algorithm>
using namespace std;
#define ll long long
ll a,b,p,sum,f[100005];
bool x[100005];
ll fd(ll x){return (f[x]==x)?x:(f[x]=fd(f[x]));}
int main()
{
	scanf("%lld %lld %lld",&a,&b,&p);
	sum=b-a+1;
	for(ll i=a;i<=b;i++)f[i]=i;
	for(ll i=2;i<=b;i++)
	{
		if(!x[i])
		{
			if(i>=p)
			{
				for(ll j=i*2;j<=b;j+=i)
				{
					x[j]=true;
					if(j-i>=a&&fd(j)!=fd(j-i))
					{
						f[fd(j)]=fd(j-i);
						sum--;
					}
				}
			}
			else for(ll j=i*2;j<=b;j+=i)x[i]=true;
		}
	}
	printf("%lld",sum); 
	return 0;
}