#include<bits/stdc++.h>
using namespace std;
int main()
{
	int a;
	cin>>a;
	double qwq=a*1.0/(a+90)*100;
	printf("%.0lf%%",qwq);
	return 0;
}

注意用printf的时候不能写%，要写%%。

#include<bits/stdc++.h>
#define int long long
#define INF 0x3f3f3f
using namespace std;
int n;
signed main(){
	cin>>n;
	printf("%.0lf%%",n/(90.0+n)*100.0);
	return 0;
}

#include<bits/stdc++.h>
#define int double
using namespace std;
signed main(){
	int n;
	cin>>n;
	n=n/(n+90.0)*100.0;
	cout<<round(n)<<'%';
}