#include <bits/stdc++.h>

using namespace std;

char v[2000005];

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