#include <iostream>
#include <cstdio>
using namespace std;
char prim[20000];
int main()
{
    freopen("ciur.in", "r", stdin);
    //freopen("ciur.out", "w", stdout);
    int n,cnt=0, i,j;
    scanf("%d", &n);
    for (i = 2; i <= n; ++i)
        prim[i] = 1;
    for (i = 2; i <= n; ++i)
        if (prim[i])
        {
            ++cnt;
            for (j = i+i; j <= n; j += i)
                prim[j] = 0;
        }
        printf("%d\n", cnt);
    return 0;

}