#include <stdio.h>
FILE *f,*g;
int n, nr;
char prim[20000005];

int main()
{
int i, j;

f=fopen("ciur.in","r");
g=fopen("ciur.out","w");

fscanf(f,"%d", &n);
for (i = 2; i <= n; ++i)
prim[i] = 1;
for (i = 2; i <= n; ++i)
if (prim[i])
{
++nr;
for (j = i+i; j <= n; j += i)
prim[j] = 0;
}
fprintf(g,"%d\n", nr);
fcloseall();
return 0;
}