#include <iostream>
bool C[2000002];
int main()
{
    int n,c=1;
    std::cin >> n;
    for (int j=1;j*2<=n;j++)
    {
        C[j*2]=1;
    }
    for (int i=3;i<=n+1;i+=2)
    {
        if (C[i]==0) {
            c++;
            for (int j=1;j*i<=n;j++)
            {
                C[j*i]=1;
            }
        }
    }
    std::cout << c;
    return 0;
}