pascal:

program bai_giai;

uses crt;

var n:longint;

begin

clrscr;

write('nhap n:');readln(n);

write('n=',(n+1)*n/2:4:0);

readln

end.

python:

n=int(input("nhap n:"))
print("s=",(n+1)*n/2)

c++:

#include <iostream>
using namespace std;
int main()
{
    int n;
    cout<<"nhap n:";
    cin>>n;
    cout<<"s="<<(n+1)*n/2;
    return 0;
}

Pascal:

uses crt;
var n:longint;
begin
clrscr;
   write('Nhap n: ');readln(n);
   write('Tong cac so tu 1 den n: ',n*(n+1) div 2);
readln
end.

Python:

n=int(input("Nhập n: "))
print("Tong cac so tu 1 den n:",n*(n+1)//2)

C++:

#include <bits/stdc++.h>
using namespace std;

int n;

int main() {
   cout<<"Nhap n: ";cin>>n;
   cout<<"Tong cac so tu 1 den n: "<<n*(n+1)/2;
}