#include <stdio.h>
bool b[2000001];
int n;
int main()
{
    FILE *fin,*fout;
    fin=fopen("ciur.in","r");
    fout=fopen("ciur.out","w");
    fscanf(fin,"%d",&n);
    for(int i=2;i<=n;i++)
    {
        if(b[i]==0) for(int j=i;j<=n/i;j++) b[i*j]=1;
    }
    int ct=0;
    for(int i=2;i<=n;i++)
    {
        if(b[i]==0) ct++;
    }
    fprintf(fout,"%d\n",ct);
}