#include <bits/stdc++.h>

#define MaxN 2000005
#define INF 2140000000
#define MOD 1999999973

using namespace std;

FILE*IN,*OUT;

int N,Ans=0;
bool p[MaxN];
int Sieve(int L)
{
    Ans++;
    for(int i=2;i<=L;i+=2)
        p[i]=1;
    for(int i=3;i<=L;i++)
    {
        if(!p[i])
        {
            Ans++;
            for(int j=i*i;j<=L;j+=2*i)
                p[j]=1;
        }
    }
}

int main()
{
    IN=fopen("ciur.in","r");
    OUT=fopen("ciur.out","w");

    fscanf(IN,"%d",&N);

    Sieve(N);

    fprintf(OUT,"%d\n",Ans);

    return 0;
}