#include <stdio.h>
using namespace std;
int c[50000];
int main()
{
    FILE *fin,*fout;
    fin=fopen("ciur.in","r");
    fout=fopen("ciur.out","w");
    long n;
    fscanf(fin,"%ld",&n);
    c[0]=1;
    c[1]=1;
    for (int i=2;i<n;i++)
        if (c[i]==0)
            for (int j=2*i;j<n;j+=i)
                c[j]=1;
    int nr=0;
    for (int i=2;i<n;i++)
        if (c[i]==0)
            nr++;
    fprintf(fout,"%d ",nr);
    return 0;
}