#include <stdlib.h>
#include <math.h>
#include <stdio.h>
int main()
{
    bool *a;
    int n,l=0;
    freopen("ciur.in" , "rt", stdin);
    freopen("ciur.out", "wt", stdout);

    scanf("%d", &n);
    a = (bool *) malloc((n+1)*sizeof(bool));
    for(int i=2;i<=n;++i)
        a[i] = 1;
    for(int i=2;i<=sqrt(n);++i)
        if(a[i])
            for(int j=i;j<=n/i;++j)
                a[i*j] = 0;
    for(int i=2;i<=n;++i)
        if(a[i])
            l++;

    printf("%d", l);

    return 0;

}