#include<iostream>
using namespace std;
bool check(int n)
{
    if (n == 2)
        return true;
    if (n == 1 || n % 2 == 0)
        return false;
    for (int i = 3;i * i <= n;i += 2)
    {
        if (n % i == 0)
            return false;
    }
    return true;
}
int main()
{
    int n,sum=0;
    cin >> n;
    for(int i=1;i<=n;i++)
    {
        if(check(i))
            sum++;
    }
    cout << sum;
    return 0;
}
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