#include<cstdio>
#include<bitset>
using namespace std;
int N,Cnt,i,j;
bitset<2000005> viz;
int main()
{
    freopen("ciur.in","r",stdin);
    freopen("ciur.out","w",stdout);
    scanf("%d",&N); Cnt=1;
    for(i=3;i*i<=N;i+=2)
        if(!viz[i]) {Cnt++; for(j=i*i;j<=N;j+=i) viz[j]=1;}
    for(;i<=N;i+=2) if(!viz[i]) Cnt++;
    printf("%d\n",Cnt);
    return 0;
}