#include <stdio.h>
#include <string.h>
#define SIZE_VALUE 1000005

int main(){
    bool prime[SIZE_VALUE];
    int i,count=0,input;
    memset(prime,0,sizeof(prime));
    for(i=2;i*i<SIZE_VALUE;i++){
        if(prime[i]==0)
        for(int j=i*i;j<SIZE_VALUE;j+=i){
            prime[j]=1;
        }
    }
    while(scanf("%d",&input)==1){
        count=0;
    for(i=2;i<=input;i++){
        if(prime[i]==0)
            count++;
    }
    printf("%d\n",count);
    }
    return 0;
}