#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]==1)
        {
            for (j = i; j <= n/i; j++)
                prim[j*i] = 0;
        }
     for(int i=2; i<=n; i++)
            if(prim[i])
            cnt++;
        printf("%d\n", cnt);
    return 0;
}