int main(){ freopen("coin.in", "r", stdin);freopen("coin.out", "w", stdout);int n,i,j;scanf("%d", &n);int ans = 0, count=0;i=1;for(i=1;i<=n;i++){ for(j=1;j<=i;j++){ ans+=i;count++;if(count==n){ printf("%d", ans);fclose(stdin);fclose(std...