#include <iostream>
#include <cstdio>
char p[100];
using namespace std;

int main()
{
    int n,i,j,c=0;
    freopen("ciur.in", "r", stdin);
    freopen("ciur.out", "w", stdout);
    scanf("%d", &n);
for (i = 2; i <= n; i++)
        p[i] = 1;
    for (i = 2; i <= n; i++)
        if (p[i])
        {
            ++c;
            for (j = i+i; j <= n; j += i)
                p[j] = 0;
        }
    printf("%d\n", c);
    return 0;
}