#include <fstream>
using namespace std;
ifstream fin("ciur.in");
ofstream fout("ciur.out");

int n, cnt;
bool ciur[2000005];

int main()
{
    int i, j;

    fin>>n;
    for (i = 2; i <= n; ++i)
        ciur[i] = 1;
    for (i = 2; i <= n; ++i)
        if (ciur[i])
        {
            ++cnt;
            for (j = i+i; j <= n; j = j + i)
                ciur[j] = 0;
        }

    fout<<cnt;

    return 0;
}