Adding CSES solution

CSES/Missing Coin Sum.cpp

@@ -0,0 +1,41 @@
+#include<bits/stdc++.h>
+#include<iostream>
+using namespace std;
+
+
+#define pp pair<ll,ll>
+#define all(x) (x).begin(), (x).end()
+typedef long long int ll;
+
+const int mxn = 2e5+10;
+
+ll b[mxn];
+ll a[mxn];
+
+void subMain(){
+    ll n;
+    cin >> n;
+    for(ll i = 0; i < n; i++){
+        cin >> a[i];
+    }
+    sort(a, a+n);
+    ll cnt = 1;
+    for(ll i = 0; i < n && a[i] <= cnt; i++){
+        cnt += a[i];
+    }
+    cout << cnt << "\n";
+}
+
+int32_t main(){
+
+	ios_base::sync_with_stdio(false);
+	cin.tie(0); cout.tie(0);
+
+
+	/*ll t;
+	cin >> t;
+	while(t--){
+        subMain();
+	}*/
+	subMain();
+}