#include using namespace std; using ll = long long; using P = pair; #define fix(x) fixed << setprecision(x) #define asc(x) x, vector, greater #define rep(i, n) for(ll i = 0; i < n; i++) #define all(x) (x).begin(),(x).end() templatebool chmin(T&a, const T&b){if(a>b){a=b;return 1;}return 0;} templatebool chmax(T&a, const T&b){if(a> n; ll x = -1, cnt = 0, ans = 0; rep(i,n+1){ int a; if(i> a; else a = -1; if(a-x==1) cnt++; else{ ans += cnt * (cnt+1) / 2; cnt = 0; } x = a; } cout << ans << '\n'; return 0; }