#include<cstdio>
#include<cmath>
using namespace std;
int main()
{
    FILE *fin=fopen("ciur.in","r"),*fout=fopen("ciur.out","w");
    int n,i,f,s,j;
    bool v[2000001]={0};
    fscanf(fin,"%d",&n);
    f=(int)sqrt((float)n);
    v[0]=v[1]=1;
    for (i=2;i<=f;++i)
        if (!v[i])
            for (j=i*i;j<=n;j+=i)
                v[j]=1;
    s=0;
    for (i=2;i<=n;++i)
        if (!v[i])
            ++s;
    fprintf(fout,"%d\n",s);
    fclose(fin);
    fclose(fout);
    return 0;
}