Submission

PPPPPPPPPP

Score: 100

User: ftm

Problemset: สามสหาย

Language: cpp

Time: 0.007 second

Submitted On: 2025-03-20 15:26:06

#include<bits/stdc++.h>
using namespace std;
#define f(i,a,b,c) for(int i=a;i<=b;i+=c)
#define r(i,a,b,c) for(int i=a;i>=b;i-=c)
#define fi first
#define se second
#define pb push_back
using ll=long long int;
using pii=pair<int,int>;
const int N=5001;
const int M=1e9+7;
int p[3*N];
vector<int> v;

int main(){
	ios::sync_with_stdio(0); cin.tie(0);
	p[0]=p[1]=1;
	for(int i=2;i*i<=3*N;i++){
		if(!p[i]){
			for(int j=i*i;j<=3*N;j+=i){
				p[j]=1;
			}
		}
	}
	int a,b;cin>>a>>b;
	for(int i=3;i<=3*N;i+=2) {
		if(i>3*b) break;
		if(i>=3*a && !p[i]) v.pb(i);
	}
	ll ans=0;
	for(auto e:v){
		for(int i=a;i<=b;i++){
			if(e-i<2*i) break;
			int x=e-3*i;
			int u=b-i;
			int x2=(x+1)/2;
			if(u>=x2) ans+=min(u,x)-x2+1;
			//cout<<e<<" "<<i<<" "<<u<<" "<<x2<<" "<<u-x2+1<<"\n";
		}
	}
	cout<<ans;
}
/*
3 6
6
/////////
400 1000

*/