n = int(input())  
l = [1 for x in range(n+1)] 
m = int(n**0.5)
for i in range(2,m+1):
    if(l[i]):
        for j in range(i*i,n+1,i):
            l[j] = 0  
cnt = 0           
for i in range(2,n+1):
    if(l[i]):
        cnt += 1       
print(cnt)