#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);
    compus[2]=0;
    for(int i=2;i<=n;i++)
        if (!compus[i])
            for(int k=i;k<=n/i;k++)
                compus[i*k]=1;
    int nPrime=0;
    for(int i=2;i<=n;i++)
        if (!compus[i]) nPrime++;
    f=fopen("ciur.out", "w");
    fprintf(f,"%d", nPrime);
}