#include<cstdio>

#define N 1999999

int main()
{
    bool c[N+1];
    static int n,nr;

    freopen("ciur.in","r",stdin);
    freopen("ciur.out","w",stdout);
    scanf("%d",&n);
    for(int i=2; i*i<=n; i++)
    {
        if(!c[i])
        {
            for(int j=i*i; j<=n; j+=i)
            {
                c[j]=true;
            }
        }
    }
    for(int i=2; i<=n; i++)
    {
        if(!c[i])
        {
            nr++;
        }
    }
    printf("%d",nr);

    return 0;
}