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区间筛质数模板题

#include <bits/stdc++.h>
#define inf 2333333333333333
#define N 1000010
#define p(a) putchar(a)
#define For(i,a,b) for(long long i=a;i<=b;++i)
//by war
//2021.1.29
using namespace std;
long long T,l,r,n,t,k,cnt,ans,temp;
long long prime[N];
bool vis[N];
void in(long long &x){
    long long y=1;char c=getchar();x=0;
    while(c<'0'||c>'9'){if(c=='-')y=-1;c=getchar();}
    while(c<='9'&&c>='0'){ x=(x<<1)+(x<<3)+c-'0';c=getchar();}
    x*=y;
}
void o(long long x){
    if(x<0){p('-');x=-x;}
    if(x>9)o(x/10);
    p(x%10+'0');
}

void Euler(){
    vis[1]=1;
    For(i,2,1e6){
        if(!vis[i]) prime[++cnt]=i;
        for(long long j=1;j<=cnt&&i*prime[j]<=1e6;j++){
            vis[i*prime[j]]=1;
            if(i%prime[j]==0) break;
        }
    }
}

signed main(){
    in(T);
    Euler();
    while(T--){
        in(l);in(r);t=sqrt(r);
        For(i,0,r-l) vis[i]=0;
        For(i,1,cnt){
            if(prime[i]>t) break;
            k=max((long long)2,l/prime[i]+(l%prime[i]!=0));
            For(j,k,inf){
                if(j*prime[i]>r) break;
                vis[j*prime[i]-l]=1;
            }
        }
        ans=0;
        For(i,0,r-l) ans+=(vis[i]==0);
        if(l==1) ans--;
        printf("Case %lld: %lld
",++temp,ans);
    }
    return 0;
}