Cod sursa(job #1698206)
Utilizator | Robert Trifan trifangrobert | Data | 3 mai 2016 23:00:04 |
---|---|---|---|
Problema | Ciurul lui Eratosthenes | Scor | 90 |
Compilator | cpp | Status | done |
Runda | Arhiva educationala | Marime | 0.59 kb |
#include <iostream>
#include <fstream>
using namespace std;
bool v[2000010];
int ciur[1000000],nciur;
int main()
{
ifstream f("ciur.in");
ofstream g("ciur.out");
int N;
f>>N;
f.close();
ciur[++nciur]=2;
for(int i=3;i<=2000000;i+=2)
{
if(v[i]==false)
{
ciur[++nciur]=i;
if(1LL*i*i<=2000000LL)
for(int k=i;k*i<=2000000;k+=2)
v[k*i]=true;
}
}
int k=0;
for(int i=1;ciur[i]<=N;i++)
k++;
g<<k<<"\n";
g.close();
return 0;
}