#include <fstream>

using namespace std;
ifstream in("ciur.in");
ofstream out("ciur.out");
int v[200000002]={1,1};
int main()
{
    int n,cnt=0;
    long long i,j;
    in>>n;
    for(i=2;i*i<=n;i++)
        if(v[i]==0)
        for(j=i*i;j<=n;j+=i)
            v[j]=1;
    for(i=2;i<=n;i++)
        if(v[i]==0)
            cnt++;
    out<<cnt;
    return 0;
}