#include <iostream>
#include <cstdio>

using namespace std;

int ciur[2000001];

int main()
{
    freopen("ciur.in","r",stdin);
    freopen("ciur.out","w",stdout);
    int n,s=0;
    scanf("%d",&n);
    for(int i=2;i<=n;i++)
        if(ciur[i]==0)
    {
        s++;
        for(int d=i*2;d<=n;d+=i)
            ciur[d]=1;
    }

    printf("%d",s);
    return 0;
}