#include <stdio.h>
#include <stdlib.h>

char v[2000000];
int n,nr,i,j;

int main()
{
    freopen("ciur.in","r",stdin);
    freopen("ciur.out","w",stdout);

    scanf("%d",&n);

    for(i=2;i<=n;i++){
        if(v[i]=='1'){
            continue;
        }else{
            nr++;
            for(j=i;j<=n;j+=i){
                v[j]='1';
            }
        }
    }
    printf("%d",nr);
    return 0;
}