#include <cstdio>
#include <cmath>
#include <cstring>
using namespace std;

int n;

void ciur(){
    bool p[n+1];
    memset(p,0,sizeof(p));

    int i = 2, l = sqrt(n);
    while(i <= l)
    {
        while( p[i] )i++;
        for(int j=i*i;j<=n;j+=i) p[j] = 1;
        i++;
    }
    int nr = 0;
    for(int i=2;i<=n;i++)
    if( !p[i] ) nr++;

        printf("%d\n",nr);
}


int main(){
    freopen("ciur.in","r",stdin);
    freopen("ciur.out","w",stdout);
        scanf("%d",&n);
        ciur();

    return 0;
}