#include<cstdio>
int n,i,j,v[2000001],np;
FILE *f,*g;
int main(){
	f=fopen("ciur.in","r");
	g=fopen("ciur.out","w");
	fscanf(f,"%d",&n);
	for(i=2;i<=n;i++){
		v[i]=1;
	}
	np=0;
	for(i=2;i<=n;i++){
		if(v[i]==1){
			for(j=2*i;j<=n;j+=i){
				v[j]=0;
			}
			np++;
		}
	}
	fprintf(g,"%d",np);
	fclose(f);
	fclose(g);
return 0;
}