Cod sursa(job #766937)
Utilizator | Data | 12 iulie 2012 15:02:29 | |
---|---|---|---|
Problema | Ciurul lui Eratosthenes | Scor | 100 |
Compilator | cpp | Status | done |
Runda | Arhiva educationala | Marime | 0.49 kb |
#include <iostream>
#include<fstream>
#include<bitset>
using namespace std;
ifstream f("ciur.in");
ofstream g("ciur.out");
int n,i,j,m,k,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++;k=2*i+1;
for(j=2*i*(i+1);j<=m;j+=k)
p[j]=1;
}
}
for(;i<=m;i++)
if(!p[i])
sol++;
g<<sol;
return 0;
}