#include <cstdio>

using namespace std;

int n,nr;
char p[2000005];

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

    int i,j;
    scanf("%d",&n);
    for(i=2;i<=n;i++)
        if(!p[i])
            {
                nr++;
                for(j=2*i;j<=n;j+=i)
                    p[j]=1;
            }
    printf("%d",nr);

    return 0;
}