#include <stdio.h>

int N, cnt;
char prim[2000005]; 
	
int main(void)
	
{
    int i, j;	
	
    freopen("ciur.in", "r", stdin);
    freopen("ciur.out", "w", stdout);
	
    scanf("%d", &N);
	
    for (i = 2; i <= N; ++i)
        prim[i] = 1;
	
    for (i = 2; i <= N; ++i)
        if (prim[i])
        {
            ++cnt;
            for (j = i+i; j <= N; j += i)
                prim[j] = 0;
        }
	
    printf("%d\n", cnt);
	
    return 0;
	
}