#include<stdio.h>
using namespace std;
long long n;bool sw[2000001];
int ciur(long int n)
{   int k=0; long long i,j;
    for(i=2;i<=n;i++)
    {
        if(sw[i]==0)
           {
                for(j=i*i;j<=n;j+=i)
                    sw[j]=1;
                k++;
           }
    }

    return k;
}
int main()
{
    FILE*fin=fopen("ciur.in","r");
    fscanf(fin,"%d",&n);
    fclose(fin);
    FILE*fout=fopen("ciur.out","w");
    fprintf(fout,"%d",ciur(n));
    return 0;
}