#include <stdio.h>

long long v[2000000];

int main()
{
    long long n=0,i=0,p=0,j=0;
    freopen("ciur.in","r",stdin);
    freopen("ciur.out","w",stdout);
    scanf("%lld",&n);
    for (i=2; i<=n; ++i) v[i]=i;
    for (i=2; i<=n; ++i)
    if (v[i]!=0)
    {
        for (j=2*i; j<=n; j+=i) v[j]=0;
        ++p;
    }
    printf("%d",p);
    return 0;
}