#include <stdio.h>

FILE *c = fopen("ciur.in","r"),*s = fopen("ciur.out","w");
long long n,prime,v[1000001],i,h;

int main()
{
    fscanf(c,"%d",&n);
    for(i=1;i<=n;i++)
        v[i] = 1;

   for(i=2;i<=n;i++)
        if(v[i])
            for(h=i+i;h<=n;h+=i)
                v[h] = 0;

    for(i=2;i<=n;i++)
        prime += v[i];
    fprintf(s,"%d",prime);
    fclose(c);
    fclose(s);
    return 0;
}