#include <stdio.h>

FILE *fin, *fout;
char ciur[2000001];
int main()
{
    fin= fopen("ciur.in","r");
    fout= fopen("ciur.out","w");
    int n,count=0,i,j;
    ciur[0]=ciur[1]=1;
    fscanf(fin,"%d",&n);
    for(i=4;i<=n;i=i+2)
        ciur[i]=1;
    for(i=3;i*i<=n;i++)
    if(!ciur[i])
        for(j=i*2;j<=n;j=j+i)
            ciur[j]=1;
    for(i=1;i<=n;i++)
        if(ciur[i]==0)
            count++;

    fprintf(fout,"%d ",count);
    fclose(fin);
    fclose(fout);
    return 0;
}