#include <stdio.h>
static int v[20000000];
int main()
{
static int n, i, j, c;
FILE *f;

f = fopen("ciur.in","rt");
fscanf(f,"%d",&n);
fclose(f);
f = fopen("ciur.out","wt");

for (i = 2; i <= n; i++)
    if(v[i] == 0)
    {
        c++;
        for (j = i+i; j <= n; j += i)
            v[j] = 1;
    }

fprintf(f,"%d",c);

fclose(f);

return 0;
}