#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
int main() {
ll x,y;scanf("%lld %lld",&x,&y);
ll sum=0,z=0;
while(sum<x+y){sum+=++z;}
if(x+y!=sum)return !printf("-1");
ll ans=0;
while(x>0){ans++,x-=z--;}
printf("%lld",ans);
return 0;
}
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