#include<cstdio>
using namespace std;
bool prim[2000001];
int main(){
	int n,nr=1,i,j;
	FILE * pFile;
	pFile=fopen("ciur.in","r");
	fscanf(pFile,"%d",&n);
	prim[2]=1;
	for(i=3;i<=n;i=i+2)
		prim[i]=1;
	for(i=3;i<=n;i=i+2){
		if(prim[i]){
			nr++;
			for(j=i+i;j<=n;j=j+i)
				prim[j]=0;
		}
	}
	pFile=fopen("ciur.out","w");
	fprintf(pFile,"%d\n",nr);
	return 0;
}