#include <stdio.h>
#include <stdlib.h>
#include <ctype.h>
#include <math.h>
#include <string.h>
#include <assert.h>
#pragma warning(disable:4996)
typedef long long LL;
int primes[10000010] = {0};//primes[0]计数
int vis[10000010] = {0};
void initprimes(int *primetable,int *visit,int n){
    int i,j;
    for(i = 2;i <= n;i++){
        if(!visit[i]){
            primetable[++primetable[0]] = i;
        }
        for(j = 1;j <= primetable[0] && i * primetable[j] <= n;j++){
            vis[i * primes[j]] = 1;
            if(i % primes[j] == 0)break;
        }
    }
}
void *lowerbound(void *base,void *key,size_t count,size_t itemsize,int(*compare)(const void *,const void *)){
    assert(base && compare);
    size_t lo = 0,hi = count - 1,mid = 0;
    if(compare(key,(char *)base + hi * itemsize) > 0){
        return (char *)base + count * itemsize;
    }
    char *pmid = 0;
    while(lo < hi){
        mid = (lo + hi) >> 1;
        pmid = ((char *)base) + mid * itemsize;
        if(compare(pmid,key) < 0){
            lo = mid + 1;
        }
        else{
            hi = mid;
        }
    }
    return (char *)base + lo * itemsize;
}
void *upperbound(void *base,void *key,size_t count,size_t itemsize,int(*compare)(const void *,const void *)){
    assert(base && compare);
    size_t lo = 0,hi = count - 1,mid;
    if(compare(key,(char *)base + hi * itemsize) >= 0){
        return (char *)base + count * itemsize;
    }
    char *pmid = 0;
    while(lo < hi){
        mid = (lo + hi) >> 1;
        char *pmid = ((char *)base) + mid * itemsize;
        if(compare(pmid,key) <= 0){
            lo = mid + 1;
        }
        else{
            hi = mid;
        }
    }
    return (char *)base + lo * itemsize;
}
int cmp(const void *a,const void *b){
    int p = *(int *)a,q = *(int *)b;
    if(p > q)return 1;
    else if(p < q)return -1;
    else return 0;
}
int main(){
#ifdef _DEBUG
    freopen("input.txt","r",stdin);
#ifdef OFILE
    freopen("test.txt","w",stdout);
#endif
#endif
    int n;
    initprimes(primes,vis,10000000);
    while(~scanf("%d",&n)){
        int pos = (int *)upperbound(primes + 1,&n,primes[0],sizeof(int),cmp) - primes - 1;
        printf("%d\n",pos);
    }
#ifdef _DEBUG
    freopen("CON","r",stdin);
#ifdef OFILE
    freopen("CON","w",stdout);
#endif
    system("pause");
#endif
    return 0;
}