#include<stdio.h>
int n,a[2000001];
void solve(){
    int i,j,k=0;
    scanf("%d",&n);
    for(i=2; i<=n; ++i)
        if(!a[i]){
            ++k;
            for(j=2*i; j<=n; j+=i)
                a[j]=1;}
    printf("%d",k);}
int main(){
    freopen("ciur.in","r",stdin);
    freopen("ciur.out","w",stdout);
    solve();
    return 0;}