#include <cstdio>

using namespace std;
char p[2000000];
int Ciurul_lui_Eratosthenes(int n)
{
    int nr=0;
    int i,j;

    for(i=2;i<=n;i++){
            if(p[i]==0){
        for(j=i*2;j<=n;j=j+i)
            p[j]=1;
            nr++;}
    }
    return nr;
}
int main()
{int i,j,nr,n;
freopen("ciur.in","r",stdin);
freopen("ciur.out","w",stdout);
scanf("%d",&n);
nr=Ciurul_lui_Eratosthenes(n);
printf("%d",nr);

    return 0;
}