#include<stdio.h>

long  n,i,j,nr;
char a[50000];

int main()
{
	freopen("ciur.in","r",stdin);
	freopen("ciur.out","w",stdout);
	scanf("%ld",&n);
	for(i=2;i<=n;i++)
		{
        	j=i+1;
			while(j<=n)
			{
				if(j%i==0)
					a[j]=1;
                j++;
            }
		}


	for(i=2;i<=n;i++)
		if(a[i]==0)nr++;

    printf("%ld",nr);
    return 0;
}