#include<stdio.h>

bool v[200001];

int main(){
    int n,i,j,nr=0;
    freopen("ciur.in","r",stdin);
    freopen("ciur.out","w",stdout);
    scanf("%d",&n);
    for(i=2;i*i<=n;i++){
        if(!v[i])
            for(j=i*i;j<=n;j+=i)
                v[j]=true;
    }
    for(i=2;i<=n;i++)
        if(!v[i]) nr++;
    printf("%d",nr);
    return 0;
}