Cod sursa(job #766402)
Utilizator | Data | 11 iulie 2012 11:01:42 | |
---|---|---|---|
Problema | Ciurul lui Eratosthenes | Scor | 10 |
Compilator | cpp | Status | done |
Runda | Arhiva educationala | Marime | 0.48 kb |
#include <iostream>
#include<fstream>
#include<bitset>
using namespace std;
ifstream f("ciur.in");
ofstream g("ciur.out");
int n,i,j,m,sol;
bitset<1000010> p;
int main()
{
f>>n;
sol=1;
if(n%2==0)n--;m=(n-1)/2;
for(i=1;2*i*(i+1)<=m;i++)
{
if(!p[i])
{
sol++;
for(j=2*i*(i+1);j<=m;j+=i)
p[j]=1;
}
}
for(;i<=m;i++)
if(!p[i])
sol++;
g<<sol;
return 0;
}