#include <stdio.h>

int n, prime, c[2000005], i, j;

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

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