Contest1331/A.cpp

//
// Created by jal on 2019-05-01.
//

#include<bits/stdc++.h>
using namespace std;
int main(){
    int l,r;
    cin >> l >> r;
    int n = r - l + 1;
    vector<bool>a(n, true);
    vector<int>prime;
    int m = sqrt(r);
    vector<bool>f(m+1, true);
    for(int i = 2; i <= m; i++){
        if(f[i]){
            prime.push_back(i);
        }
        for(int j = 0; j < prime.size() && prime[j]*i <= m; j++){
            f[prime[j]*i] = false;
        }
    }
    for(int i = 0; i < prime.size(); i ++){
        int k = prime[i];
        for(int j = max(2, (l + k - 1) / k * k); j <= r; j+= k){
            a[j-l] = false;
        }
    }
    cout << accumulate(a.begin(), a.end(), 0) << endl;
}

//2100000000 2101000000