1 .

n=int(input())
s=0
for i in range(1,n+1):
    s+=i 
print(s)

2 .

import math 
n=int(input());
Ok= True ;
if n==2 : Ok = True ;
if n < 2 : 
    Ok = False ;
else :
    for i in range (2,n-1) :
        if n % i ==0 :
            Ok = False 
            break ;
print(Ok)

3 .

n=int(input());
d=0;
for i in range(1,n):
    if n%i==0 : 
        d+=i ;
if d == n :
    print(True);
else :
    print(False);

1.
n = int(input())
s = 0
for i in range(1,n+1):
    s+=i
print(s)
2.
n = int(input())
d = 0
for i in range(1,n+1):
    if n%i==0:
        d+=1
if d==2:
    print("YES")
else:
    print("NO")
3.
n = int(input())
s = 0
for i in range(1,n):
    if n%i==0:
        s += i
if s==n:
    print("YES")
else:
    print("NO")