#include <cstdio>
using namespace std;
int n,nr,i,j;
bool v[2000005];
int main()
{
    freopen("ciur.in", "r", stdin);
    freopen("ciur.out", "w", stdout);
    scanf("%d", &n);

    v[0]=v[1]=1;
    for(i=2;i*i<=n;i++)
    {
        if(v[i]==0)
        {
            for(j=i;j<=n/i;j++)
                v[i*j]=1;
        }
    }
    for(i=2;i<=n;i++)
        if(v[i]==0)
            nr++;
    printf("%d",nr);
    return 0;
}