#include"stdio.h"
long n,q=1,pr[500000];

int prim(const long r)
{for(long g=0;pr[g]*pr[g]<=r;g++)if(r%pr[g]==0)return 0;
pr[q]=r;return 1;}

void genprime(const long n)
{for(long g=2;pr[q-1]<=n;g++)q+=prim(g);q-=2;}

int main()
{pr[0]=2;freopen("ciur.in","r",stdin);freopen("ciur.out","w",stdout);scanf("%ld",&n);genprime(n);printf("%ld",q);
return 0;}