#include <cstdio>
#include <bitset>

using namespace std;

bitset <2000005> prime;

int n, nrprime;

void ciur()
{
    int i, j;
    for (i = 2; i <= n ; i++)
        if (prime[i] == 0)
        {
            nrprime++;
            if (i * i <= n)
                for (j = i + i; j <= n; j += i)
                    prime[j] = 1;
        }
}

int main()
{
    FILE *in, *out;
    in = fopen("ciur.in", "r");
    out = fopen("ciur.out","w");
    int n, nrprime;
    fscanf(in,"%d",&n);
    ciur();
    fprintf(out,"%d", nrprime);
    return 0;
}