#include <stdio.h>

FILE *c = fopen("ciur.in","r"),*s = fopen("ciur.out","w");
int n,prime=0,i,h;
char v[2000002];

int main()
{
    fscanf(c,"%d",&n);
   for(i=2;i<=n;i++)
        if(v[i]==0)
        {
            prime++;
            for(h=i+i;h<=n;h+=i)
                v[h] = 1;
        }
    fprintf(s,"%d",prime);
    fclose(c);
    fclose(s);
    return 0;
}