#include <cstdio>
FILE *f=fopen("ciur.in","r");
FILE *g=fopen("ciur.out","w");
char ciur[2000000];
int isprime;
int n;
void faciur()
{
    int i,j;
    if(n>=2)isprime++;
    for(i=1;2*i+1<=n;i++)
        if(ciur[2*i+1]==0)
        {
            isprime++;
            for(j=1;(2*j+1)*(2*i+1)<=n;j++)
                ciur[(2*j+1)*(2*i+1)]=1;
        }
}

int main()
{
    fscanf(f,"%d",&n);
        faciur();
    fprintf(g,"%d",isprime);
    return 0;
}