#include <stdio.h>
long i,n,mul;
int nr_p;
int main()
{
    FILE *f1,*f2;
    f1=fopen("ciur.in","r");
    f2=fopen("ciur.out","w");
    fscanf(f1,"%ld",&n);
    bool v[n+1];
    for(i=2;i<=n;i++)
    {
        if(v[i]==0)
        {
            nr_p++;
            mul=i;
            while(mul<=n)
            {
                v[mul]=1;
                mul+=i;
            }
        }
    }
    fprintf(f2,"%d",nr_p);
    return 0;
}