#include <cstdio>
using namespace std;
FILE *f1=fopen("ciur.in","r"),*f2=fopen("ciur.out","w");
int n, cnt;
bool prim[2000005];
int main()
{
    int i,j;
    fscanf(f1,"%d",&n);
    prim[1]=1;
    for(i=2;i<=n;++i)
        if(!prim[i])
        {
            ++cnt;
            for(j=i+i;j<=n;j+=i)prim[j]=1;
        }
    fprintf(f2,"%d",cnt);
    return 0;
    fclose(f1);
    fclose(f2);
}