#include<stdio.h>
int i,j,nr,n,v[2000000];
int main()
{freopen("ciur.in","r",stdin);
freopen("ciur.out","w",stdout);
scanf("%d",&n);
if(n>=2)
{v[2]=1;nr=1;
for(i=3;i<=n;i+=2)
	v[i]=1;
for(i=3;i<=n;i+=2)
	if(v[i])
	{nr++;
	for(j=i*i;j<=n;j=j+i)
		v[j]=0;
	}
}
printf("%d",nr);
}