#include <stdio.h>
#include <string.h>
int N,cnt;
char prim[2000005];
int main(void)
{
    int i,j;
    freopen("ciur.in", "r", stdin);
    freopen("ciur.out", "w", stdout);
    scanf("%d",&N);
    for(i=2;i<=N;i++)
        prim[i]=1;
    for(i=2;i<=N;i++)
        if(prim[i])
        {
            cnt++;
            for(j=i+1;j<=N;j+=i)
                prim[j]=0;
        }
    printf("%d",cnt-1);
}