0
1
mirror of https://git.sb/baoshuo/OI-codes.git synced 2024-12-24 03:31:59 +00:00
OI-codes/Luogu/problem/P3912/P3912.cpp

24 lines
458 B
C++
Raw Normal View History

2020-11-02 11:59:20 +00:00
#include <bits/stdc++.h>
using namespace std;
int main() {
int n;
cin >> n;
int s = n-1;
bool prime[100000005];
memset(prime, 0, sizeof(prime));
for(int i = 2 ; i*i <= n ; i++) {
if(!prime[i]) {
for(int j = i*2 ; j <= n ; j+= i) {
if(!prime[j]) {
prime[j] = true;
s--;
}
}
}
}
cout << s << endl;
return 0;
}