#include<cstdio>
#define _NMAX 2000010
using namespace std;
int n;
bool compus[_NMAX];

int main()
{
    FILE *f=fopen("ciur.in", "r");
    fscanf(f,"%d",&n);
    int nPrime=1;
    compus[3]=0;
    for(int i=3;i<=n;i+=2)
        if (!compus[i])
        {
            nPrime++;
            for(long long k=i*i;k<=n;k+=i)
                compus[k]=1;
        }
    f=fopen("ciur.out", "w");
    fprintf(f,"%d", nPrime);
}