#includebits/stdc++.h using namespace std; const int maxn=5e5+ 10 ; #define ll long long int a[maxn],b[maxn]; ll c[maxn]; int n; ll ask( int x) { ll ans = 0 ; for (; x; x-=x- x) ans += c[x]; return ans; } void add( int x, int y) { for (; x=
#include<bits/stdc++.h>
using namespace std; const int maxn=5e5+10; #define ll long long
int a[maxn],b[maxn]; ll c[maxn]; int n; ll ask(int x) { ll ans=0; for(; x; x-=x&-x) ans+=c[x]; return ans; } void add(int x,int y) { for(; x<=n; x+=x&-x) c[x]+=y; } int main() { scanf("%d",&n); for(int i=1; i<=n; i++) { scanf("%d",&a[i]); b[i]=a[i]; } sort(b+1,b+1+n); int cnt=unique(b+1,b+1+n)-b-1; ll ans=0; for(int i=1;i<=n;i++) a[i]=lower_bound(b+1,b+1+cnt,a[i])-b; for(int i=n; i>=1; i--) { ans=ans+ask(a[i]-1); add(a[i],1); } printf("%lld",ans); }