#include<stdio.h>

long n,i,j,nr;
char s[2000001];

int main(void){

freopen("ciur.in","r",stdin);
freopen("ciur.out","w",stdout);
scanf("%ld",&n);

for(i=2; i<=n; i++)if(s[i]!='p'){nr++; for(j=i; j<=n; j+=i)s[j]='p'; } 
printf("%ld",nr);

return 0;
}