#include <iostream>
#include <fstream>
#include <bitset>

using namespace std;
int n;
bitset<2000005> b;
void solve()
{
    b[1]=1;
    int nr=0;
    for(int k=2;k<=n;k++)
        if(b[k]==0)
            {nr++;
            for(int i=k;i<=n;i+=k)
                b[i]=1;}
    printf("%d ",nr);
}
int main()
{
    freopen("ciur.in","r",stdin);
    freopen("ciur.out","w",stdout);
    scanf("%d ",&n);
    solve();
    return 0;
}