Cod sursa(job #2527731)
Utilizator | Tudor Pasca Tudor_Pasca | Data | 20 ianuarie 2020 20:36:26 |
---|---|---|---|
Problema | Ciurul lui Eratosthenes | Scor | 100 |
Compilator | cpp-64 | Status | done |
Runda | Arhiva educationala | Marime | 0.5 kb |
#include <iostream>
#include <fstream>
using namespace std;
ifstream in("ciur.in");
ofstream out("ciur.out");
int n, cont;
bool ciur[2000001];
void ciuruiala()
{
for(int j = 4; j <= n; j += 2)
ciur[j] = 1;
for(int i = 3; i*i <= n; i+=2)
for(int j = i*i; j <= n; j += i)
ciur[j] = 1;
}
int main()
{
in >> n;
ciuruiala();
for(int i = 2; i <= n; i++)
cont += (!ciur[i]);
out << cont << '\n';
return 0;
}