#include <bits/stdc++.h>
#define longc 2000005
using namespace std;

char verif[longc];

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