#include<cstdio>
using namespace std;
bool prim[2000001];
int n,nr;
int ciur()
{
    prim[1]=1;
    prim[0]=1;
    for(int i=2;i<=n/2;i++)
        if(prim[i]==0)for(int j=i;j<=n;j+=i) prim[j]=1;
    for(int i=1;i<=n;i++) if(!prim[i]) nr++;
}
int main()
{
    FILE *fin,*fout;
    fin=fopen("ciur.in","r");
    fout=fopen("ciur.out","w");
    fscanf(fin,"%d",&n);
    ciur();
    printf("%d",nr);
}