#include<stdio.h>

#define nmax 2000003

int a[nmax],x;

int main()
{
    long n;
    FILE *f=fopen("ciur.in","r");
    FILE *g=fopen("ciur.out","w");
    fscanf(f,"%ld",&n);
    for(long i=2;i<=n;++i)
             if (a[i]==0)
                {
                for(long j=2*i;j<=n;j+=i) a[j]=1;
                x++;
                }
    fprintf(g,"%d",x);
    return 0;
}