#include <cstdio>

using namespace std;
int k,x,i,j;
bool v[2000000];
int main()
{
    freopen("ciur.in","r",stdin);
    freopen("ciur.out","w",stdout);
    scanf("%d",&x);
    k=0;
    for(i=2;i<=x;i++)
    {
        if(v[i]==0)
        {
            k++;
            for(j=2;j<=x/i;j++)
            v[i*j]=1;
        }
    }
    printf("%d",k);
    return 0;
}