Cod sursa(job #3215825)
Utilizator | Dumitru Robert Ionut robert_dumitru | Data | 15 martie 2024 13:15:58 |
---|---|---|---|
Problema | Ciurul lui Eratosthenes | Scor | 10 |
Compilator | cpp-64 | Status | done |
Runda | Arhiva educationala | Marime | 0.45 kb |
#include <bits/stdc++.h>
using namespace std;
ifstream fin("ciur.in");
ofstream fout("ciur.out");
int n;
bitset<2000005> b;
void Ciur()
{
b[1] = 1;
for (int i = 4; i <= n; i += 2)
b[i] = 1;
for (int i = 3; i * i <= n; i += 2)
if (b[i] == 0)
for (int j = i * i; j <= n; j += 2 * i)
b[i] = 1;
}
int main()
{
fin >> n;
Ciur();
fout << n - b.count();
return 0;
}