#include <cstdio>

using namespace std;

char p[2000002];
int n,nr;

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

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