#include <stdio.h>
using namespace std;
int N, p[2000005], nr;

int main()
{
    freopen("ciur.in", "r", stdin);
    freopen("ciur.out", "w", stdout);
    scanf("%d", &N);
    nr++;
    for(int i = 3; i <= N; i += 2)
        if(!p[i])
        {
            nr++;
            for(int j = i*i; j <= N; j += i + i)
                p[j] = 1;
        }
    printf("%d\n", nr);
    return 0;
}