深夜无事可干啊
#include<bits/stdc++.h>
using namespace std;
const int maxn = 1e6+11;
typedef long long ll;
bitset<maxn> isnprime;
int prime[maxn];
int sai(int n){
isnprime[0]=isnprime[1]=1;
for(int i = 2; i*i <= n; i++){
if(!isnprime[i]){
for(int j = 2*i; j <= n; j+=i){
isnprime[j]=1;
}
}
}
int cnt=0;
for(int i = 1; i <= n; i++) if(!isnprime[i]) prime[cnt++]=i;
return cnt;
}
bitset<maxn> vis;
int main(){
int cntt=sai(maxn-1);
int T,kase=0; scanf("%d",&T);
while(T--){
int a,b; scanf("%d%d",&a,&b);
int cnt=0;
if(b<maxn) for(int i = a; i <= b; i++){
cnt+=1-isnprime[i];
}
else{
for(int i = 0; i <= b-a; i++) vis[i]=0;
for(int i = 0; i < cntt && prime[i]*prime[i]<=b; i++){
ll k = a/prime[i];
if(k*prime[i]<a) k++;//internal
for(ll j = k*prime[i]; j <= b; j+=prime[i]) vis[j-a]=1;
}
for(ll i = a; i <= b; i++) cnt+=1-vis[i-a];
}
printf("Case %d: %d\n",++kase,cnt);
}
return 0;
}