#include <stdio.h>

int n,v[2000005],nrp;

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