#include <cstdio>

using namespace std;

int n;
int nr;
int a[2000010];

int main()
{
    freopen("ciur.in", "r", stdin);
    freopen("ciur.out", "w", stdout);

    scanf("%d", &n);
    for(int i = 2; i <= n; ++ i){
        if(a[i] == 0){
            nr ++;
            int j = i + i;
            while(j <= n){
                a[j] = 1;
                j += i;
            }
        }
    }
    printf("%d\n", nr);

    return 0;
}