https://www.codechef.com/JAN21C/problems/DECODEIT SISGEV error problem

https://www.codechef.com/JAN21C/problems/DECODEIT

< #include <bits/stdc++.h>
#include
using namespace std;
typedef long long int lli;

char alpha(int x)
{
char arr1[16]={‘a’,‘b’,‘c’,‘d’,‘e’,‘f’,‘g’,‘h’,‘i’,‘j’,‘k’,‘l’,‘m’,‘n’,‘o’,‘p’};
return arr1[x];
}

int main() {
int t;
std::cin >> t;
while(t–)
{
lli n;
std::cin >> n;
lli i=n/4;
string S;
cin>>S;
lli j=0;
for(j=0;j<i;j++)
{
lli y =j*4;
string susS = S.substr(y,y+4);
int x = stoi(susS,0,2);
char c= alpha(x);
cout<<c;

        }
    cout<<endl;
    
}
return 0;

}>

why am i getting segmentation fault even though logic is correct