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Cod sursa(job #751607)
#include <fstream>
using namespace std;
ifstream in("ciur.in");
ofstream out("ciur.out");
const int N=2000000;
bool c[N];
int ciur (int n)
{
int nr = 0;
for (int i=2;i*i<=n;i++)
if (!c[i])//i prim/*
for(int j=i*i; j<=n;j+=i)
c[j]=true;
for (int i=2;i<=n;i++)
if (!c[i]) nr++;
return nr;
}
int main()
{
int nr , n ;
in>>n;
nr = ciur (n);
out<<nr;
return 0;
}