#include<stdio.h>
int main()
{   freopen("ciur.in","r",stdin);
    freopen("ciur.out","w",stdout);
    char v[2000001];
    long m=0,n;
    scanf("%d",&n);
    for(int i=2;i<=n;i++)
    {
            v[i]='0';
    }
    for(long i=2;i<=n;++i)
    {
            if(v[i]=='0')
            {
            for(int i2=i;i2<=n;i2=i2+i)
            {
                    v[i2]='1';
            }
            ++m;
            }
    }
    printf("%d",m);
    
    return 0;
}