#include<cstdio>
int j,nr,n,i;
bool a[2000000];
int main()
{
    freopen("ciur.in","r",stdin);
    freopen("ciur.out","w",stdout);
    scanf("%d",&n);
    a[0]=1;
    a[1]=1;
    for(i=3;i<=n;i+=2)
    {
        if(a[i]==0)
        {
            nr++;
            for(j=i+i;j<=n;j+=i)
                a[j]=1;
        }
    }
    printf("%d",nr+1);
    return 0;
}