#include <fstream>

using namespace std;
ifstream fin("ciur.in");
ofstream fout("ciur.out");
int ciur[2000001];
int main()
{

    int n, i, j,m;
    fin >> n;
    for (i = 0; i <= n; ++i)
        ciur[i] = 1;
    for (i = 2; i <= n; ++i) {
        if (ciur[i] == 0) {
            for (j = i * i; j <= n; j = j + i)
                ciur[j] = 1;
                    }
            }
    for(i=1;i<=n;i++)
    {
        if(ciur[i]==0)
            m++;
    }
    fout<<m;
    return 0;
}