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