Language: C++

#pragma comment(linker, "/stack:200000000")
#pragma GCC optimize("Ofast")
#pragma GCC target("sse,sse2,sse3,ssse3,sse4,avx,avx2")

#include<bits/stdc++.h>
#include <ext/pb_ds/detail/standard_policies.hpp>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
using namespace std;
using namespace __gnu_pbds;

#define fastio              ios_base::sync_with_stdio(false); cin.tie(NULL); cout.tie(NULL);
#define int                 long long
#define ll                  long long
#define ld                  long double
#define vi                  vector<int>
#define pii                 pair<int,int>
#define vpii                vector< pair<int,int> >
#define uset                unordered_set
#define umap                unordered_map
#define maxpq               priority_queue<int>
#define minpq               priority_queue<int,vi,greater<int>()>

#define all(v)              v.begin(),v.end()
#define part(v,s,e)         v.begin()+s,v.begin()+e
#define rev(v)              reverse(v.begin(),v.end())
#define sz(x)               (int)x.size()
#define def(v)              memset(v,-1,sizeof(v));
#define def0(v)             memset(v,0,sizeof(v));
#define minv(a)             *min_element(all(a))
#define maxv(a)             *max_element(all(a))
#define sumv(a)             accumulate(all(a),0)

#define lb                  lower_bound         //returns the index of the next smallest number just greater than or equal to that number.
#define ub                  upper_bound         //returns the index of the first element in the range [first, last) that is greater than value, or last if no such element is found.
#define desc                greater<int>()
#define pb                  emplace_back
#define mp                  make_pair
#define F                   first
#define S                   second

#define mod                 1000000007
#define inf                 1000000000000000
#define infty               1000000000000000000LL
#define md                  998244353
#define PI                  acos(-1.0)
#define endl                "\n"
#define rr                  return
#define br                  cout<<"\n";
#define hr                  for(int i=0;i<40;i++)    cout<<"-";cout<<endl;

#define gcd(a,b)            __gcd(a,b)
#define lcm(a,b)            (a/(__gcd(a,b)))*b

#define setbits(x)          __builtin_popcountll(x)
#define leadzero(x)         __builtin_clzll(x)
#define trailzero(x)        __builtin_ctzll(x)

#define ip(v)               for(auto& i:v)    cin>>i;
#define op(v)               for(auto i:v)    cout<<i<<" ";cout<<endl;
#define deb(x)              cout <<"Value of " #x << " : " << x << endl;

#define ordered_set         tree<int,null_type,less<int>,rb_tree_tag,tree_order_statistics_node_update>


#ifndef ONLINE_JUDGE
#define dbg(...) __f(#__VA_ARGS__, __VA_ARGS__)
template <typename Arg1>
void __f(const char* name, Arg1&& arg1) {cout << name << " : " << arg1 << endl;}
template <typename Arg1, typename... Args>
void __f(const char* names, Arg1&& arg1, Args&&... args) {
    const char* comma = strchr(names + 1, ',');
    cout.write(names, comma - names) << " : " << arg1 << "  ";
    __f(comma + 1, args...);
}
#else
#define dbg(...) 50
#endif



bool comp(pii a,pii b)
{
    return a.F>=b.F;
}

print(vpii v)
{
    int n=v.size();
    for(int j=0;j<n;j++)
        cout<<v[j].F<<" "<<v[j].S<<endl;
}
    
void solve()
{    
    
    int n;
    cin>>n;

    int ans=0;

    ans=(n+999)/1000*1000;
    cout<<ans-n<<endl;

}    

int32_t main()
{

    fastio
    cout<<setprecision(15)<<fixed;

    #ifndef ONLINE_JUDGE
        freopen("input.txt","r",stdin);
        freopen("output.txt","w",stdout);
        freopen("error.txt","w",stderr);
    #endif

    int t=1;
    // cin>>t;

    for(int i=1;i<=t;i++)
    {
        // cout<<"Case #"<<i<<" : "<<endl;
        solve();
    }
    
    #ifndef ONLINE_JUDGE    
        cerr<<"time taken : "<<(float)clock()/CLOCKS_PER_SEC<<" secs"<<endl;
    #endif

    return 0;
}

Compiler output:
a.cc:87:1: error: ISO C++ forbids declaration of 'print' with no type [-fpermissive]
   87 | print(vpii v)
      | ^~~~~
a.cc: In function 'int print(std::vector<std::pair<long long int, long long int> >)':
a.cc:92:1: warning: no return statement in function returning non-void [-Wreturn-type]
   92 | }
      | ^