#include<bits/stdc++.h>
using namespace std;
#define m 5800000
#define m1 100000000
bool f[m1];
int n,cnt=0,p[m];
int main(){
    scanf("%d",&n);
    for(int i=2;i<=n;i++){
        if(!f[i]){
            p[++cnt]=i;
		}
		for(int j=1;j<=cnt;j++){
            if(i*p[j]>n)break;
			f[i*p[j]]=1;
            if(!(i%p[j]))break;
		}
    }
    printf("%d",cnt);
    return 0;
}