#include <stdio.h>


using namespace std;

int v[2000005];
int n,cnt;
int main()

{
    freopen("ciur.in", "r", stdin);
    freopen("ciur.out", "w", stdout);
    scanf("%d", &n);
    for ( int i = 2 ; i <= n; ++i)
        {
            if (!v[i] )
            {
                ++cnt;
                for ( int j = i+i; j <= n ; j = j + i)
                    v[j] = 1;
            }
        }
        printf("%d\n", cnt);

    return 0;
}