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<code class="language-cpp">#include <bits/stdc++.h>
using namespace std;

int jisuan(long long n)
{
	for(long long i=2;i*i<=n;++i)
		if(n%i==0) return false;
    return true;
    
}


int main()
{
	long long n,sum=0;
	cin>>n;
    for(long long i=2;i<=n;++i)
        if(jisuan(i)) ++sum;
	cout<<sum;
	return 0;
}
</code>