Cod sursa(job #2504038)
Utilizator | Data | 4 decembrie 2019 11:42:48 | |
---|---|---|---|
Problema | Ciurul lui Eratosthenes | Scor | 100 |
Compilator | cpp-64 | Status | done |
Runda | Arhiva educationala | Marime | 0.46 kb |
#include <fstream>
using namespace std;
const int N=2000001;
bool c[N];
int main()
{
ifstream fin("ciur.in");
ofstream fout("ciur.out");
int n;
fin>>n;
c[0]=c[1]=true;
for(int i=2;i*i<=n;i++){
if(!c[i]){
for(int j=i*i;j<=n;j+=i){
c[j]=true;
}
}
}
int cnt=0;
for(int i=2;i<=n;i++){
if(!c[i]) cnt++;
}
fout<<cnt;
fin.close();
fout.close();
return 0;
}