#include <cstdio>
using namespace std;
const int NMAX = 2000000;
const int base = 32;
int ciur[(NMAX >> 6) + 5];
int main()
{
    freopen("ciur.in", "r", stdin);
    freopen("ciur.out", "w", stdout);
    int n, nr, i, j;
    nr = 1;
    scanf("%d", &n);
    for(i = 3 ; i * i <= n ; i += 2)
        if( !(ciur[i / (2 * base)] & (1 << (i % base))) )
        {
            for(j = i * i ; j <= n ; j += (i << 1))
                ciur[j / (2 * base)] |= (1 << (j % base));
            nr ++;
        }
    printf("%d\n", nr);
    return 0;
}