#include <cstdio>
char v[2000005];
int n,cnt;
void citire()
{
    scanf("%d", &n);
}
void ciur()
{
    int i,j;
    v[0]=1;
    v[1]=1;
    for(i=2;i<=n;++i)
        if(v[i]==NULL)
            for(j=i+i;j<=n;j+=i)
                v[j]=1;
    cnt=0;
    for(i=2;i<=n;++i)
        if(v[i]==NULL)
            ++cnt;
}
void afisare()
{
    printf("%d\n", cnt);
}
void rezolva_problema()
{
    citire();
    ciur();
    afisare();
}
int main()
{
    freopen("ciur.in", "r", stdin);
    freopen("ciur.out", "w", stdout);
    rezolva_problema();
    return 0;
}