#include <cstdio>

using namespace std;

#define VMAX 2000005
#define NMAX 300001

int N,i=1,prime[NMAX];
bool prim[VMAX];

void ciur()
{
    int i,j;

    for (i=2;i<VMAX;++i)
    {
        if (prim[i]) continue;
        prime[++prime[0]]=i;

        for (j=2*i;j<VMAX;j+=i) prim[j]=true;
    }

}

int main()
{
freopen("ciur.in","r",stdin);
freopen("ciur.out","w",stdout);

ciur();

scanf("%d",&N);

while (prime[i]<=N) ++i;

printf("%d\n",i-1);

return 0;
}