#include<cstdio>
#include<cmath>
using namespace std;
bool v[2000001];
void eratostene(int n)
{
    int i,j,lim;
    v[0]=v[1]=1;
    for(i=4;i<=n;i=i+2)
        v[i]=1;
    lim=(int)sqrt((double)n);
    for(i=3;i<=lim;i++)
        if(v[i]==0)
            for(j=i*i;j<=n;j=j+2*i)
                v[j]=1;
}
int main()
{
    int n,i,nr=0;
    freopen("ciur.in","r",stdin);
    freopen("ciur.out","w",stdout);
    scanf("%d",&n);
    eratostene(2000000);
    for(i=2;i<n;i++)
        if(v[i]==0)
            nr++;
    printf("%d",nr);
}