#include<stdio.h>
#define NMAX 2000005
long n,i,j,nr;
bool v[NMAX];
int main()
{
    freopen("ciur.in","r",stdin);
    freopen("ciur.out","w",stdout);
    scanf("%ld",&n);
    for(i=2;i<=n;i++)
        if(v[i]==false)
            for(j=2;j*i<=n;j++)
                v[i*j]=true;
    for(i=2;i<=n;i++)
        if(v[i]==false)
            nr++;
    printf("%ld",nr);
    return 0;
}