#include <cstdio>

using namespace std;

int p[2000002],n,nr;

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

    scanf("%d",&n);

    p[1]=1;

    for(int i=2;i<n;i++)
    {
        for(int j=i+i;j<n;j+=i)
        {
            p[j]=1;
        }
    }
    for(int i=1;i<n;i++)
        if(p[i]==0)
            nr++;
    printf("%d",nr);
    return 0;
}