#include <fstream>

using namespace std;
ifstream fin("ciur.in");
ofstream fout("ciur.out");

bool IsntPrime[2000005];

int main()
{
    int i, j, ct = 0, n, x;

    fin >> n;

    for(i = 2; i <=n; i++)
    {
        if(!IsntPrime[i]){
            ct++; x = i;
            for(j = i; j <= n; j = j + x)
                IsntPrime[j] = 1;
        }
    }

    fout << ct;

    return 0;
}